A system-level analysis of the effectiveness of special education was conducted in an educational cooperative comprised of six school districts. In total, 96 students (grades 1-6) were assessed three times during the year on direct, curriculum-based measures of achievement in math, reading, and spelling. Analyses of student performance data were conducted across the entire cooperative for each district, by teacher, and finally by classification, grade, and sex of student. In contrast to previous findings, the data indicated that special education had a positive effect on student achievement and resulted in performance levels closer to those attained by regular education students. The benefits of such a data-based assessment approach include a measurement alternative for the student as well as a comprehensive reviewing procedure for the needs and problems of the school system. (Author/CL)