The purpose of this study was to determine whether there were significant differences in the academic achievement of children attending three different types of school: a model "open" school, a comparable "traditional" school, and a traditional school with a student population from a higher socioeconomic area. Data based on standardized achievement tests (Comprehensive Test of Basic Skills, CTBS) were gathered from approximately 95 third graders over a two-year period for each of the three schools. In addition, a control for intelligence was obtained by analyzing a discrepancy score based on predicted achievement, rather than actual grade equivalent. One way analysis of variance on discrepancy scores revealed significant differences for the subtests of Reference, favoring the model "open" school, and Social Studies, favoring the higher socioeconomic "traditional" school. Analysis of discrepancy scores, collected at the beginning and end of a two-year period, showed five out of the seven CTBS subtests favored the model school. The study stressed the importance of examining not only the method of instruction, but also the socioeconomic factor and the teacher variable. (Author/MP)