We used multiple probe design with probe trials across three teacher-student dyads to examine the effects of a professional development on middle school general education teachers' accurate use of simultaneous prompting procedure and self-monitoring as well as the effects of the simultaneous prompting procedure on acquisition of academic core content of middle school students with developmental disabilities in inclusive classrooms. Moreover, we investigated the maintenance and generalization effects of professional development on teachers' outcomes as well as simultaneous prompting procedure on students' outcomes. Last, teachers' and students' opinions regarding social validity of the study were investigated. Results showed that (a) teachers acquired using simultaneous prompting procedure and self-monitoring with 100% accuracy, maintained the acquired teaching behaviors over time and generalized them across different conditions and (b) students acquired their targeted academic content, maintained them over time, and generalized them across different people. Moreover, both the opinions of teachers and the students were positive. Implication of the findings and directions for future research are discussed.