Younger age is associated with better outcomes in autism severity, language, and adaptive skills after one school year in autism special education classes

A well-accepted hypothesis in the field of autism spectrum disorder (ASD) is that early intervention is crucial for better outcomes. However, research has noted significant variability in early intervention outcomes. This study examined the role of age in relation to outcomes in comprehensive developmental domains following one year of school in community special education classes for ASD. We compared two groups: a younger group (n = 35) aged 34–59 months and an older group (n = 38) aged 60–91 months. The groups did not differ in cognitive ability, autism severity or adaptive behavioral skills at the start of the school year. After one year, the entire study population showed significant progress in all developmental domains. However, changes in effect size were much more robust in the younger ASD group. Only younger children showed a significant decrease in the severity of communication, awareness and restricted interests and repetitive behavior subdomains and a significant increase in motor adaptive skills. Younger children also showed more remarkable improvement in the naming and expressive subdomains. Respectively, older age predicted more severe ASD symptoms at the end of the educational year. Corresponding to brain plasticity theories, our findings point to an association between age and outcomes. The findings should serve as a benchmark for policymakers regarding early intervention in young children with autism.