Background: There are few well validated brief measures that can be used to assess the general progress of young children with autism spectrum disorders (ASD) over time. In the present study, the Autism Treatment Evaluation Checklist (ATEC) was used as part of a comprehensive assessment battery to monitor the progress of 22 school-aged children with ASD who had previously taken part in intensive home- or school-based intervention programmes in their pre-school years. Methods: Parents completed the ATEC when the children were on average 5.5 years and then again 5-6 years later (mean age 10.4 years). Standardised measures were also used to assess cognitive, language and adaptive behaviour skills and severity of autism symptoms over the same period. Results: The ATEC had high internal consistency at both time points. ATEC total and sub-scale scores remained relatively stable over time and were highly and significantly correlated with cognitive, language and adaptive behaviour skills and severity of autism symptoms at both assessment points. Initial ATEC total scores predicted 64% of the variance in scores at the subsequent follow-up. However, there was also considerable variation in the patterns of scores shown by individual children over time. Conclusions: This study provides some preliminary evidence of the ATEC's potential value for monitoring progress of children with ASD over time. Its advantages and limitations are discussed in the context of the need systematically to monitor the progress of children with ASD over time or in response to intervention.