The paper describes the stages in development of an assessment of the adaptive behaviour skills of children in Bangladesh. Item selection and reduction are described, based on an ecological analysis of behaviours expected of children aged between two and nine years of age, living in both urban and rural settings. The IBAS has four major subscales: motor skills, socialisation, communication and daily living skills. Norms have been constructed based on testing a nationally representative sample of 1404 children. Content, construct and discriminant validity are established, and the reliability of the total scale and subscales is high, both between testers and over time. The IBAS can provide a baseline indication of level of skills in a child with intellectual disability, and aid in planning an appropriate curriculum-based programme in discussion with the child's family.