Prescription Learning is a multi-media diagnostic prescriptive program providing individualized instruction using six instructional strategies. Nine elementary schools and four middle schools in the Portland Public School District used Prescriptive Learning to provide supplemental reading and math instruction to low-performing students. Selected by Chapter 1 eligibility requirements, 1,223 students, in grades K-8, received services (973 students in reading and 779 in math). This report evaluates the Prescriptive Learning program by comparing the achievement gains of 1983-84 program students with: (1) other district Chapter 1 students; (2) all district students; and (3) 1982-83 program students. The Comprehensive Tests of Basic Skills, (Grade 2) and the Portland Achievement Levels Tests (Grades 3 to 8) measured student achievement. In addition, program coordinators were interviewed about implementation procedures and students' opinions were surveyed. Findings include: (1) generally greater achievement gains were achieved by first year Prescriptive Learning students over their pre-program year; (2) both Prescriptive Learning and other Chapter 1 treatments assisted students; (3) two-year students' achievement growth rate was lower than one-year students; and (4) computers were the most popular lab station with students. Appendices contain: (1) new primary reading skills continuums; (2) reading materials evaluations; and (3) growth tables for Prescriptive Learning and Chapter 1 students by grade. (BS)