A study was conducted to determine (1) the extent to which the degree of use of PRI/RS (the Prescriptive Reading Inventory Reading Systems, a criterion referenced management system developed by CTB/McGraw Hill) affected comparable groups of students on standardized achievement measures; (2) whether the degree of use differentially influenced students' achievement based on their initial ability levels; and (3) the extent to which differential use of PRI/RS and TRACER, a computer management system, affected reading acquisition measures, such as number of objectives mastered and retention of skills mastered. Subjects were all students in grades two and five in a large city school district. Analysis of data showed that the use of PRI/RS had a systematic and reliable effect on student reading achievement. The students whose teachers used PRI/RS and TRACER consistently and to a high degree performed significantly better on standardized achievement tests. It also appeared that the effect was distributed across ability levels. At all ability levels, the high-use individuals demonstrated superior reading achievement test scores. (FL)