The number of applied behavior analysis (ABA) classrooms for students with autism is increasing in K-12 public schools. To inform instruction of students with autism in public school settings, this study examined the relation between performance on mastery learning assessments and standardized achievement tests for students with autism spectrum disorders (ASD) in an applied behavior analysis (ABA) classroom. The measures included ABLLS-R, DIBELS-R, and DIBELS-M. Results of the study indicate that all students acquired new skills across domains and met their IEP goals measured by the mastery learning assessment, but they scored low on reading and math for their grade level according to standardized achievement tests. Suggestions for prompting good autism practice in public school settings are discussed.