A demonstration project tested the efficacy of computer-assisted instruction (CAI) as a means of providing individualized in-service education in mathematics to elementary school teachers. Seventy-eight teachers were assigned to matched experimental and control groups; the former received a CAI version of the Modern Mathematics (Modmath) course on a system which used an IBM 7010-1448 computer configuration along with IBM 1052 Typewriter Consoles and IBM 1051 Control Units. The control group took a conventional lecture version of the course. Posttest results and observations indicated no significant differences between the groups with respect to achievement in math, attitude toward math, or teaching behavior in the classroom. CAI thus appeared to be a viable means of presenting in-service in mathematics since teachers using the program performed as well as those in the control group. It is likely that CAI has greater promise for the future because the programs can be further individualized to meet the specific in-service needs of teachers. Technical difficulties encountered were minimal and the results of the project were disseminated widely. (PB)