Various models of school effects on student achievement were applied in a study of reading and mathematics achievement in the 94 schools of the Oklahoma City Public Schools. The Leadership/Climate Inventory, completed by 1294 teachers, rated school principals in the areas of expectations, instructional leadership, forceful or dynamic style, effective consultation with others, discipline, resources, time management, and evaluation of results. Data were also collected on the allocation and use of instructional time at each school. Achievement data, aggregated to the school level, were based on reading and mathematics scores on the California Achievement Tests. Models have suggested that the following school effects are related to achievement--principals' leadership effectiveness, within-school cohesiveness among teachers, prior achievement in the school and instructional time. Path analysis was used to study these relationships, as well as differences between upper and lower grades. Results supported the principal effects and within-school cohesiveness models, although the effects were stronger in mathematics than in reading. Effects were also stronger in the elementary and fifth year grades than in the middle schools and high schools. Instructional time was also related to achievement, especially in mathematics. (GDC)