High school mathematics teachers were trained to provide mastery learning instruction. A primary characteristic of this method of instruction is the feedback-corrective enrichment loop. This study was conducted to determine whether class time could be allocated for the principles of mastery learning within the fixed amount of available time without placing one group of students at a disadvantage while increasing the instruction for others. The teacher training program emphasized improving the ability to understand the principles of mastery learning and increasing the opportunities for learning effective classroom management strategies. The training activities incorporated staff development practices which would increase the likelihood that teachers would implement the instructional strategies presented. Results of the study indicated that teachers who participated in the staff development program made greater use of the feedback-corrective enrichment loop in their classroom lessons. Teachers and students utilized available instruction time more purposefully. This study does not support Marshall Arlin's contention that group based mastery learning programs deprive the academically rich to provide corrective instruction for the academically poor. (DWH)