In this exploratory multiple case study, it is examined how a computer game focused on improving ineffective learning behavior can be used as a tool to assess, improve, and study real-time mouse behavior (MB) in different types of children: 18 children (3.8–6.3 years) with Autistic Spectrum Disorder (ASD), Attention Deficit/Hyperactivity Disorder (ADHD), or comorbid ASD and ADHD, and 5 effectively learning (EL) children (3.5–3.8 years). The children's MB processes, for example “Errors” and “Reaction times,” were interpreted in terms of executive functions (EFs). Trajectories of averaged MB were compared among the groups of ASD, ADHD, comorbid, and EL children. Clinical groups showed differences in their MB, which were similar to the expected differences based on EF tests. In addition, a case study of a typical ASD, ADHD, and EL child was included in order to demonstrate typical individual MB patterns across time. MB processes might therefore provide a window into the processes of EF (dys)functioning.