Purpose: The study objective was to determine if the validated Behavioral Inflexibility Scale (BIS) is sensitive to the detection of developmental changes in inflexibility in a sample of autistic children. Methods: Parents of autistic children (n = 146, 3-17 years) completed the BIS at two time points, one year apart, to examine change. Results: The findings indicate the BIS is sensitive to the detection of developmental changes and that child-level variables are not associated with those changes. Children's Time 1 BIS scores predicted children's severity on an independent outcome measure. Finally, a relationship between total services children were receiving and change in BIS scores over time was not found. Conclusion: The findings suggest the BIS is a reasonable candidate for consideration as an outcome measure.