Families with neurodevelopmental disorders engage in varied types of therapies to address behavioural, communication and cognitive challenges. Research suggests that consistent therapy adherence predicts positive therapy outcomes. The present study examined therapy adherence in 55 parent-child dyads where all children had been diagnosed with ASD, ADHD, and/or ID. Parents completed questionnaires assessing demographics, therapy type, adherence to child treatment, parental stress, and challenging child behaviour. The researchers proposed a new scale, the Child Therapy Adherence Scale (CTAS), which initial testing supported as a reliable measure of therapy adherence. Significant relationships were found between parental stress, annual household income and therapy adherence, with parental stress being a notably strong predictor of therapy adherence. No significant relationships were observed between child challenging behaviour, single parent status and therapy adherence. These findings have implications for practitioners, in that parent levels of stress and demographic influences may impact capacity to adhere to recommended home practice and interventions for children with neurodevelopmental disorders.