This project was designed to study the effects of an inservice model on the quantity and quality of developmental mathematics instruction provided by participating teachers. Participants were seven teachers of students in grades from 2 to 6 who had volunteered for the project after being selected as potential lead teachers in mathematics. The inservice consisted of teacher observations, group inservice on effective teaching, individual planning and recommendations for becoming more effective, demonstration teaching, and more observations together with feedback and discussion. The results indicate that these seven elementary teachers increased the quantity of their developmental instruction to about half of their class period, from about 11 minutes each day to about 20 minutes each day. The inservice model also had a positive effect on the quality of the developmental instruction provided: teachers attended to more details related to instruction, used models more often, and used process questions to assess student understanding more effectively. As an inservice model, the one used in this project has the potential of effectively changing the behavior of teachers and improving instruction. Appendices contain samples of postobservation feedback for grades 4 and 6, papers on teaching mathematics concepts and algorithms, and an administrator/teacher feedback questionnaire. (Author/MNS)