The adoption by Seattle (Washington) Public Schools of the Prescriptive Reading Inventory Reading System (PRI-RS) was a decision driven by the district's commitment to effective schooling. The PRI-RS is a criterion referenced approach to the instruction and assessment of reading skills, and it consists of five levels, A through E, coordinated with grade levels. The evaluation reported here consists of three major activities: (1) a statistical analysis of a district-wide data base, including demographic PRI use, and achievement data on more than 31,000 students; (2) structured interviews with principals and teachers in six schools in the district; and (3) an analysis of curricular match among PRI, California Achievement Test (CAT), and school reading curricula. Results indicate that: (1) the use of the PRI was highest for the early grades and significantly lower in Grades 7 and 8; (2) the average student in Grades 1-6 took five to six mastery tests before Spring CAT testing; (3) the frequency of PRI use was not a significant determinant of reading or language arts achievement gains; (4) quality PRI use was associated with achievement gains in reading or language arts; (5) PRI instructional materials contain many good items, but require extra work to implement; (6) effective classroom management strategies are critical in using the system well; and (7) the TRACER reporting system is burdensome and error-filled. (TJH)