Parental engagement in early intervention for infants with cerebral palsy—A realist synthesis

Abstract Background Emphasis on parental engagement strategies within occupational therapy and physiotherapy early intervention (EI) programmes for infants at high risk of cerebral palsy (CP) has increased. This reflects consensus that increasing parent participation enhances treatment efficacy, potentially improving infant and parent outcomes. However, evaluation of parental engagement in EI is complex. Despite the growing application of parental engagement strategies, aligned with family‐centred care practice, theoretical evaluation is currently lacking within the literature. This realist synthesis aimed to identify component theories underlying EI strategies to support parental engagement and to use empirical findings to evaluate how these work in practice. Methods Realist synthesis: Databases Medline, Embase, Amed, CINAHL and PsychInfo were searched (from February 1985 ‐ February 2020); further articles were sourced from reference lists. A data extraction form was used, and a Critical Appraisal Skills Programme tool was used to assess study rigour. Results Twenty‐six articles were included. Quality of relationships, parent education and intervention co‐design were the key themes related to parental engagement strategies. Findings indicate that constructive parent reasoning mechanisms of trust, belief, sense of control, perceived feasibility of home programme delivery and ultimately motivation are linked to the underlying intervention resources afforded by specific strategies (e.g., coaching pedagogy). These responses are precursors to engagement outcomes that include increased parental self‐efficacy and adherence. Importantly, parental self‐efficacy can initiate a process of change leading to improved parental confidence and anxiety. Conclusions Sensitively designed programme strategies, centred on relational quality between parent, infant and therapist, are fundamental for effective parent connection, involvement and investment within EI for infants with CP.


| INTRODUCTION
Advances in developmental follow-up assessments and clinical pathways has enabled earlier identification of infants at high risk of cerebral palsy (CP), in order to expedite referral to early intervention (EI) services (Novak et al., 2017). In this paper, EI describes targeted occupational therapy and physiotherapy (OPT) treatment for infants aged under 24 months, with understanding that intervention within this period could mitigate against the functional impact of a cerebral lesion at a time when neuroplasticity is heightened (Kolb et al., 2011;Morgan, Novak, et al., 2016). Such habilitation relies upon extensive repetition through trial-and-error opportunities (Hadders-Algra, 2011).
For example, learning to walk requires infants to take on average 2368 steps per hour with 17 falls per hour (Adolph et al., 2012).
Constraint-induced movement therapy (CIMT) also demonstrates the intensity that functional recovery requires (Gordon, 2011).
Focus on parental engagement within EI delivery has increased within a family centred care (FCC) framework, as opposed to therapist-led child focused models of EI that have provided inconclusive outcomes in clinical research King & Chiarello, 2014;Morgan, Darrah, et al., 2016). Parental engagement shifts emphasis away from reliance on professionally dominated services, which are usually sporadic in nature, towards parents who have significantly more opportunities for interaction with their infants (Lord et al., 2018). Interventions with successful home translation by parents may promote greater therapy intensity, required for improved infant outcome (Mahoney & Perales, 2006).
Outcomes of parental engagement in therapy delivery are not limited to infants, with potential benefits including parental learning and wellbeing (Lord et al., 2018).
Conceptualizing parental engagement for evaluation is difficult.
Adherence to intervention programmes is a relevant outcome but is only one component of engagement. Authors have described engagement as a co-constructed process of 'connection, involvement and investment' (Mattingly & Fleming, 1994). Others have divided parental engagement into multiple components including affective (e.g., receptiveness), cognitive (e.g., willingness) and behavioural (e.g., self-efficacy) involvement within OPT intervention which motivates work on tasks outside of sessions (King et al., 2019). Evaluation in this article will use this multiple component conceptualization and explore processes towards optimal states of parental engagement.
Parental self-efficacy (PSE), an example of one process, is defined as parents' belief in their ability to positively influence their child's development. However, parents of high-risk infants are at risk of anxiety, stress and depression due to their infant's adverse neonatal experiences; this can disrupt the parent-infant relationship (Aagaard & Hall, 2008;Benzies et al., 2013;Gibbs et al., 2015).
To date, systematic reviews in EI for infants with CP have mostly focused upon infant outcomes and are inconclusive regarding effectiveness (Hadders-Algra et al., 2017;Morgan, Darrah, et al., 2016). These reviews select controlled trials; arguably, this design provides limited theoretical evaluation around causal processes in complex EI programmes to understand 'what works, for whom and in what circumstances' for optimal parental engagement (Autti-Rämö, 2011; Pawson et al., 2005). This is likely the reason why, despite the growth of parental engagement description (with associated theory) in EI programmes, theory evaluation is lacking within the literature. Parent delivered intervention designs need well-thought-out development, clarity in implementation and sophisticated evaluation of inherent complexities, as they are embedded within open and changeable psychosocial and institutional contexts. A strong theoretical and empirical base is a prerequisite for exploring relationships between complex intervention components and outcomes (Kovach, 2009). Realist synthesis has the potential to inform EI programme development and is timely given the current gap in this field of literature.

| Realist synthesis
This review followed realist synthesis methodology guidelines (Pawson et al., 2005;Wong et al., 2013). A realist synthesis seeks to develop explanatory theory by evaluating how programme mechanisms might work in given contexts to produce outcomes. A critical analysis of causal relationships is summarized within a context, mechanism, outcome configuration (CMOc) (Pawson et al., 2005). Context refers to elements outside the formal architecture of the intervention which influence mechanisms and outcomes. Mechanisms are considered as both the resources provided through an intervention and individuals' responses, positive or negative. Interventions rely on mechanisms becoming active to achieve their effects, via individuals' input. Outcomes, intended or unintended, are produced from how people respond to resources within their context (Pawson et al., 2005).

Key Messages
• Collaborative early intervention parental involvement strategies require matching collaborative relational and communication styles for parents to rationalize trust.
• Co-designed goals and home programmes (including educational materials) with realistic time commitments will help parents to believe in EI feasibility and benefits, creating increased adherence.
• Coaching and supporting parent-infant sensitivity help parents to connect, participate and apply learning more effectively, whilst building outcomes of parental selfefficacy • Increased parenting efficacy may reinforce constructive parent reasoning responses (e.g., sense of control and motivation) to improve the underlying parental psychosocial context and sustain engagement long term.
• Stress may be an unavoidable parent response to involvement in early intervention (EI), particularly early on after neonatal trauma and adjusting to an uncertain diagnosis. were searched using relevant keywords between 1985 and February 2020 (Table 1). This period provided a comprehensive range, encompassing historical changes in EI, rendering older literature irrelevant, in addition to advances in study quality. Terms 'Involvement' OR 'Engagement' OR 'Participation' were included in the original scoping searches but as these are not widely applied MeSH terms in this field, hits were restricted to below 50 across all databases. Therefore, to optimize coverage, these keywords were removed.

| Identifying primary sources
After the initial search, duplicates were removed, and then, titles and abstracts were screened using search criteria before full text review to produce the final list of included articles, for data extraction and synthesis. The inclusion/exclusion criteria were developed using a consensus team approach. Study selection was completed by one reviewer (PH) with an agreed process that any uncertainties could be referred back to the team for a final decision regarding inclusion. Ultimately, this was not required. Thematic development involved the team, whereby each author contributed to refine and check the validity of the results and the CMOc development.

| Data extraction and appraisal
Realist syntheses include studies with different designs including qualitative, quantitative and protocol papers; therefore, a bespoke data extraction matrix was created, which is summarized in Table 3. Methodological quality was evaluated using the Critical Appraisal Skills Programme tools: Rigour classification was assigned as poor, moderate or strong.

| Developing CMO configuration
For this review, 'theory' refers to proposed explanations for how given strategies were suggested to work in practice. Initial scoping for discernible programme theories, which focused upon parental engagement strategies, were extracted from articles; either from explicit descriptions (e.g., protocol) or, where undocumented, implicit theories were inferred from the intervention architecture. The initial iteration of proposed theories were placed into categories before the subsequent synthesis (Table 2). Using empirical studies, a further iterative process highlighted relevant themes around context, mechanisms and outcomes from parent experience or outcome data pertaining to affective, cognitive or behavioural domains of engagement in parent delivered programmes. These findings were evaluated against the  '1985-2020') categories of the initial proposed theories to build the synthesis, later conceptualized within the CMOc. The CMOc construction included several iterations from the identified themes, until a level of synthesis was reached that provided an explanatory interpretation of the combined primary data. This cyclical process was conducted by one reviewer (PH), with discussion and development of each iteration with the team until the final CMOc was agreed.
Mechanisms were differentiated into resources and reasoning, worked through the parent context (Dalkin et al., 2015). We propose resources are components afforded by an intervention which are introduced into a context to produce a desired response.
Responses, often triggered on a continuum, are defined as parents' reasoning (i.e., beliefs and perceptions about resources) to initiate action.

| Intervention theories
Parental engagement theory and application has evolved within EI. Each iteration of initial proposed programme theory is summarized in Table 2, as 'quality of relationships', 'parent education' and 'codesigning intervention'. Table S1 provides the link between the original studies and these initial proposed theories. In the following section, the identified themes developed from the empirical studies are synthesized (using relevant findings) under the initial proposed theory.  (Eliasson et al., 2016;Morgan et al., 2014;Ohgi et al., 2004).
T A B L E 2 Initial iteration of proposed theories Theory one: Quality of relationships between parent, therapist and infant Trusting and collaborative relationships between parents and OPTs are foundational for effective therapy co-design and education . Supporting parent sensitivity with their infant's state regulation and behavioural cues, creates an enriched relational environment (attachment theory -Bowlby), which supports infant stability whilst also facilitating keener observation of infants' for applied sensorimotor learning (Eliasson et al., 2016;Ohgi et al., 2004).
Theory two: Parent education EI therapy education engages parents; delivered ideally within home, focus on parents learning to extend therapy provision through the family environment into daily routines (Basu, Pearse, Baggaley, Watson, & Rapley, 2017;Eliasson et al., 2016;Hielkema et al., 2010;Morgan et al., 2014;Palmer et al., 1990). Pedagogic strategy shifts to coaching; with aims to enhance families' coping strategies and autonomy development, in applying solution focused challenges to infant's development throughout family life (Eliasson et al., 2016;Hielkema et al., 2010). Programme curricula focus on applied neuromotor learning principles; inducing progressive self-produced infant activity using 'scaffolding' theory (supported progressive learning), with appropriate toy choice and handling support that is reduced upon infant initiation (Eliasson et al., 2014(Eliasson et al., , 2016Morgan et al., 2014). Home programme (paper or video) provision supports parent learning Dusing et al., 2018). Parent schedules (attentive to family constraints) or diaries foster focus and accountability (Campbell et al., 2012;Dusing et al., 2018;Hielkema et al., 2010;Morgan et al., 2014).
Theory three: Co-designing intervention Collaborative goal setting enables parents to prioritize meaningful goals for their family and guides treatment direction accordingly. Supporting parent participation, increases attention on therapy translation into daily routines (Eliasson et al., 2016;Hielkema et al., 2010;Morgan et al., 2014).

| Communication
Positive communication is fundamental for relational development.
Parental willingness to respond to programme strategies is enabled or constrained by the therapeutic relational and communication approach Holmstrom et al., 2019). Authentic verbal encouragement influences parenting confidence . Building collaborative therapeutic relationships generates parental reasoning of increased sense of control during difficult circumstances, reducing stress (Broggi & Sabatelli, 2010

| Trust
Trust is a reasoning mechanism central to collaborative therapeutic relationships (Ballantyne et al., 2019). Trusting is a significant act for these parents who describe their circumstantial instability, therefore relational continuity is vital  Intervention co-design (0-6 months age), acceptability and feasibility evaluation of programme that trains parents to deliver intervention targeting the affected side, with activities incorporated pervasively at home. Parents provided with materials including DVD and booklet. Guidance on infant selfinitiated activity on the affected side.
The intervention (including testing protocol) was acceptable to parents and practicable with daily routines.
No adverse reactions were found to the treatment in the domains of parent well-being and sense of competence.
Qualitative participatory co-design focus groups, with one-one interviews and questionnaire. Families transitioning from neonatal unit may experience initial stress of participation in EI programmes.
High adherence levels can still be sustained, by; • Adequate support of the therapist (weekly), • Accessible educational resources (8th grade educational level, including videos and photos), • Realistic daily routines (scheduled diary of 20 minutes/5 days week), • There was significant decrease in mother's state anxiety. And confidence in caregiving score increased significantly in the treatment group.
Infant motor outcomes improved more in the treatment group and were close to significance in an under-powered study. gives them greater opportunity to learn complex handling skills and transfer these into daily activities. Parents perceive expert therapy led handling treatment is more effective than their own and the least stressful option for them and their infant. But, this may lead to a greater dependence on therapy undermining parent self-efficacy.

| Greater parent-infant connection
Greater parent receptiveness can be triggered through play and relational-based therapy (Basu et al., 2017;Morgan, Novak, et al., 2016;Ohgi et al., 2004). If infants enjoy treatment participation through play, and activities are built on parental connection with their infant, then parents will invest more deeply in treatment . Ohgi et al. (2004) specifically explored incorporating parent-infant responsiveness training, meaning parents received support to observe and respond to their baby's behavioural communication cues during conventional physiotherapy. Infants receiving intervention demonstrated significantly less irritability, better state regulation and less stress; this connected to improvements in parent well-being parameters such as reduced anxiety and increased confidence. In another study, parents felt that their observational skills were enhanced to see 'tiny details' of their infant's development (Dusing et al., 2015). When integrated into EI, together with appropriate play activities, parent sensitivity supported a greater two-way enjoyment in the delivery, reinforcing parental connection (Holmstrom et al., 2019). However, introducing parent-infant support later (18 months) is not as effective (Palmer et al., 1990). Therefore, attachment theory integrated early on (<6 months age) could support outcomes of increased parent sensitivity, responsiveness, PSE and decreased maternal stress and anxiety.

| Theory 2: Parent education
EI therapy education is designed to engage parents in an active learning role. It is delivered ideally within home and focuses on parents learning to extend therapy provision through the family environment within daily routines (Basu et al., 2017;Eliasson et al., 2016;Hielkema et al., 2010;Morgan et al., 2014;Palmer et al., 1990). Pedagogic strategy now favours coaching, with aims to enhance families' autonomy development, in applying solution focused challenges to infant's development (Eliasson et al., 2016;Hielkema et al., 2010). Programme curricula focuses on neuromotor learning principles to induce progressive self-produced infant activity using 'scaffolding' theory (supported progressive learning), with appropriate toy choice (Eliasson et al., 2014(Eliasson et al., , 2016Morgan et al., 2014). Home programme (paper or video) provision supports parent learning Dusing et al., 2018). Parent schedules (attentive to family constraints) or diaries foster focus and accountability (Dusing et al., 2018;Morgan et al., 2014).

| Readiness
Fundamental to effective education is parental readiness to engage.
Yet the contextual backdrop means that circumstantial psychosocial challenges are foisted upon parents, including an emerging CP diagnosis for their baby following traumatic neonatal experiences and additional care burdens (Ballantyne et al., 2019;Basu et al., 2018).
This can negatively impact parenting confidence, parent-infant relationship development and engagement with therapy services by impinging on their affective, cognitive and behavioural involvement states . Adjustment processes to shock, grief and uncertainty are normal and are likely to continue unfolding beyond their child's infancy, with parents' initial engagement with therapists focusing on the need for information (Ballantyne et al., 2019). Parents overwhelmingly desire early, sensitive and transparent CP diagnosis disclosure, which is important for adjustment and grieving responses, although professionals are often reluctant to provide early diagnosis (Ballantyne et al., 2019;Byrne et al., 2019). Whilst processing the diagnosis, parental support networks (family, peer-to-peer and professionals) are critical for adjustment (Ballantyne et al., 2019;Gibbs et al., 2019). A research gap was identified around psychological therapies for parents at this point and specifically how this might influence engagement. Some argue that greater OPT support and preparation for families within the neonatal unit environment home transition could support readiness to engage in community EI Dusing et al., 2015). Thereafter, parental engagement within EI itself can support adjustment (Ballantyne et al., 2019).

| Parent beliefs in educational resources
Parental beliefs around pedagogy are influential. Some parents perceive therapist-led interventions as less stressful than parent participation in sessions, especially if siblings are present (Scales et al., 2007). Parent stress outcomes, as measured by psychometric assessments, do not differ between coaching and traditional therapy educational interventions (Hielkema et al., 2019). Nevertheless, parents believe their participation is more likely to make an intervention effective, whereas prolonged observer roles may create disengagement (Scales et al., 2007). Parents also believe that complex therapy handling techniques require substantial training (Ustad et al., 2009), which could undermine PSE development. However, coaching is associated with increased PSE over time (Hielkema et al., 2019).
Others have reported parental stress concerning engagement, particularly around transition to home from NICU and challenges in programme curricula Eliasson et al., 2018), which may affect parents of lower socioeconomic status more (Dusing et al., 2015). Yet, within these programmes, parents still reported programme acceptability and feasibility, supported by high adherence and satisfaction. Co-designed educational materials are vital to resonate with and motivate parents. Particular attention to language accessibility (pitched at 8th grade), use of photos and video, as well as the material quality (e.g., glossy manual), can increase parent receptiveness and learning (Basu et al., 2017Dusing et al., 2018;Morgan, Novak, et al., 2016). In addition, activity focused play-based outcome measures can positively support parent understanding, focus and connection, as planning 'scaffolded' activities becomes easier and fun .

| Adherence
Arguably, parent adherence signifies readiness and willingness, and is a useful (although limited) outcome measure of parental engagement. Adherence is higher when parents observe that infant milestones such as sitting or walking have not been met, presumably as greater awareness of the problem triggers motivation (Mattern-Baxter et al., 2013).
Parent delivered home intervention may be perceived as a burden affecting adherence levels, with increased care demands of infants with CP particularly those more severely affected .
Also, an infant's ability to engage within therapeutic activities is limited in early months (Dusing et al., 2015). Therefore, realistic expectations regarding parental time investment are necessary to make the programme workable. Some programmes have included daily time prescriptions for parent home activities, for example, 20 min 5 days per week (SPEEDI programme, [Dusing et al., 2018], 30 min 6 days per week Baby CIMT programme [Eliasson et al., 2018]) and 12 min 5 days per week (Campbell et al., 2012). Measuring against these prescribed times for parent led programmes, adherence (parent diaries) was above expected within the SPEEDI (120%) and Baby-CIMT (97%), with parents reporting favourably upon their feasibility. Conversely, Campbell et al. (2012) found that despite lower expectations around daily parent input at home (12 min), adherence was poor with parents only able to complete 5 min, 2-3 times/week (average). The authors concluded the critical factor behind the low adherence was an inadequate number of supporting therapy sessions (once/month), in contrast to the SPEEDI and Baby-CIMT programmes that provided weekly therapy sessions. This suggests that successful parent education that encourages adherence to parent delivered therapy relies on regular (i.e., weekly) face-face 45-min sessions to support parental efficacy for adherence. Accessible communication with therapists is also important for families between sessions .
Long-term adherence is another challenge. Campbell et al. (2012) found in their distributed intervention model that parent adherence regressed after 7 months of the 10-month programme. Parental contexts including busy family life, multiple children and grief, may explain why long-term home delivery is difficult to sustain in real life . Mass practice models (focused 3-4 month blocks) could allow parents to rationalize commitment, as discrete breaks allow normal family development particularly earlier in life (Dusing et al., 2015;Gibbs et al., 2019). Coaching, through enabling greater parent autonomy, is associated over time with reduced parental worry, reduced perceived time restriction and greater advocacy in relation to their child's additional needs (Hielkema et al., 2019). Therefore, coaching may support parental adjustment to diagnosis and create healthier parent perceptions of balancing time doing home therapy versus their own self-care, facilitating parent well-being and more sustainable long term engagement (Hielkema et al., 2019). Yet making causative assertions from such associations requires caution.
Self-reported adherence data has clear limitations and does not appraise learning translation objectively. Only one study evaluated fidelity of parent delivery at home (Dirks et al., 2016). Within this coaching intervention parents translated learning to home, evidenced with video observations of providing progressive motor trunk activity during bathing, which was associated with improved motor outcomes.

| Theory 3: Co-designing intervention
Collaborative goal setting enables parents to prioritize meaningful goals and guides treatment direction accordingly. Supporting parental participation within the intervention design increases their attention on therapy translation into daily routines (Eliasson et al., 2016;Hielkema et al., 2011;Morgan et al., 2014).

| Goals enhance parental engagement
Having goals and a clear plan during a time of uncertainty augments engagement, leading to greater adherence to parent delivery of home programmes compared to standard care for most parents (Morgan, Novak, et al., 2016). This is created by underlying cognitive mechanisms of belief in the intervention that are triggered by setting collaborative meaningful contextualized goals . If parental involvement is goal-directed with time expectations, incorporating pervasive strategies and scheduling congruent to home routines, then the perceived burden will reduce, translating into greater belief in the workability of intervention thus furthering adherence Dusing et al., 2018). Celebrating goal achievement can galvanize PSE and motivation, with retrospective reasoning as parents observe change following the intervention they provided and related reduced care burden Eliasson et al., 2018;Gibbs et al., 2019;Mattern-Baxter et al., 2013). Specifically, goal achievement builds fathers' PSE most effectively (Eliasson et al., 2018).

| Collaborative treatment planning
The GAME programme, versus standard care, demonstrated greater parental satisfaction and infant motor outcomes with focused collaborative goal and treatment planning, drawing the family home environmental context in to create an enriched motor programme (Morgan, Novak, et al., 2016). Collaborative treatment planning requires collaborative relationships, to increase motivation, enhance parental sense of control and reduce stress, whilst also creating a cognitive state of conviction that translation to home is possible (Broggi & Sabatelli, 2010;Holmstrom et al., 2019;King et al., 2019). Where parents' autonomous involvement is encouraged, it supports perceptions that their input is valued and validated by the therapist, therefore generating greater longitudinal engagement with programme resources (Hielkema et al., 2019;Morgan, Novak, et al., 2016).

| CONTEXT-MECHANISM-OUTCOME CONFIGURATION
The key findings of this synthesis are summarized as a CMOc ( Figure 2) to portray the multifactorial contexts and mechanisms that have potential to influence parental engagement in OPT EI. Intervention strategies that induce positive parental mechanisms and create optimal outcomes of parental engagement are outlined in Table 4.
An important consideration is the interaction between mechanism resources and reasoning. Dalkin et al. (2015, p. 4) assert that resources and reasoning are 'mutually constitutive of a mechanism' but disaggregating them enables clearer differentiation between the mechanism and context, hence our use of their reworked CMO formula. This shows how resources afforded by the intervention, sensitive to the parental pre-existing context, can work through these mitigating circumstances to create a positive response and produce desired outcomes. However, families are also living within a shifting context, which includes the adjustment of parents to an early CP diagnosis and increased awareness of the relevance of therapy due to associated missed motor milestones. This changing context can be highly influential, impacting particularly on parental reasoning within interventions, and therefore needs to be considered in relation to how the CMO interplay works. The outcome of stress (due to involvement expectations within intervention) during the first 6 months is unintended but unavoidable for some parents, due to multiple chal-

| Parental socioeconomic and educational context
Many studies revealed parent demographic contexts where socioeconomic and educational status were below population averages (Dusing et al., 2018;Hielkema et al., 2011). Lower socioeconomic and educational status is often reported as a problematic context within early years' interventions (Cunha et al., 2018 (Gordon, 2011). Yet achieving these intensities with infants at high risk of CP is more challenging. Pervasive strategies may hold the key . King and Chiarello (2014) argue that 'family-provider collaboration needs to be investigated at multiple points in the intervention process, because engagement and collaboration can change over the course of the intervention' (p.1050). Our synthesis supports this assertion. Time is an important context where early home engagement can add stress, and long-term adherence may also wane, particularly where support is insufficient. Sensitive balance is needed around parental adjustment to early CP diagnosis and readiness within EI. Therefore, the lack of research evaluating psychological support for parents during infancy is surprising (Irwin et al., 2019). Further research to understand the complexities surrounding parental states of readiness in EI (Hielkema et al., 2019) and embedding psychological support within programmes, could help understanding of how supporting parental adjustment might enhance affective components of engagement. In addition, research suggests that parent-infant dyads are compromised in the first year, where there is a CP diagnosis (Festante et al., 2019). There is strong theoretical underpinning for parent-infant support in contemporary programmes, with the logic that it mediates better outcomes in high-risk infants and parents (Hutchon et al., 2019;van Wassenaer-Leemhuis et al., 2016). Yet, more research is required to evaluate parental outcomes and causative links to motor developmental outcomes for infants with CP.
Our findings demonstrated that programme strategies were effective within contexts of lower socioeconomic and educational status but these families also reported early stress from their involvement. Other EI research for high-risk infants shows infants of families with higher social risk may benefit most from intervention but at a greater cost to mental health (Spittle et al., 2018).
Education through collaborative communication with positive professionalparent partnerships is essential and parent programme adherence outcomes were promising in many contemporary programmes. Yet measuring parent adherence seems paradoxical to an equal and collaborative therapist-parent relationship (Lawlor & Mattingly, 1998). Research is limited regarding what collaborative communication looks like in EI. One study observed parental engagement within EI analysing how parents reframe therapeutic education within their own embodied learning (Håkstad et al., 2018). Further research around parent and therapist engagement, collaborative communication and learning processes within EI could offer enlightenment for OPT education (Lawlor, 2012). Therapists would also benefit from understanding parents' individualized learning preferences to enhance resources afforded within intervention (Hurtubise & Carpenter, 2017). Ultimately, parents' motivation to learn through their active participation is interconnected with distinctive trusting therapeutic relationships, captured in related literature (Harrison et al., 2007;Hurtubise & Carpenter, 2017;Piggot et al., 2002).
Warnings exist within EI literature that good parent rapport and regular educational sessions may not always be sufficient for triggering parental adherence to home programmes, highlighting that teaching translation cannot be assumed (Badr et al., 2006

| CONCLUSION
This realist synthesis has teased apart critical mechanisms to explain how parental engagement can be optimized within OPT EI. It shows that parent reasoning responses of trust, belief, sense of control and ultimately motivation are linked to resources afforded by the programme, provided at a challenging time. Such parental reasoning is essential in creating engagement outcomes that include increased parental self-efficacy and adherence. The findings provide valuable theoretical insights to further clinical practice and research in EI.