A study was conducted to determine if different levels of implementation of an interactive videodisc-based instructional program in mathematics differentially affected the academic achievement of regular students and students with disabilities in mainstreamed classrooms. The videodisc program was designed to be controlled by a teacher in group instruction. Thirty-eight students with disabilities who normally receive mathematics instruction in a resource room, received the majority of instruction in a regular classroom. Additional instruction was provided to these students by resource room teachers using the interactive video program. Seventy-one regular education students and 38 resource students received video-based instruction in 9 fifth grade classrooms. Students were classified as high-achievers, low-achievers, and low achievers with special needs (resource students). Students were administered a criterion-referenced pretest and posttest. Data were also collected on the amount of extra help received by the resource students and on level of implementation. Teachers were divided into high, average, and low implementors of the program. The results of a two-way analysis of the covariance showed statistically and educationally significant differences in implementation level and type of student. There was also a statistically significant interaction between implementation level and type of student. This suggests that there is a strong relationship between the level of implementation and student achievement. (9 references) (Author/DB)