In this review of research findings, the authors identify ten categories of variables that may influence student learning and schools' instructional effectiveness. All the studies reviewed define effectiveness in terms of basic skills achievement, and all limit their research primarily to elementary schools and students with low socioeconomic status. The ten categories comprise (1) principals' achievement expectations and other characteristics; (2) time-related factors, such as time spent in school or time on task; (3) coordination among instructional programs; (4) teacher attitudes and other characteristics; (5) instructional materials and methods; (6) teacher-student interaction, including a discussion of reinforcement techniques; (7) basic skills acquisition; (8) instructional accountability, including teacher and student evaluation; (9) student background characteristics, including family income, race, or residence; and (10) organizational variables such as class size or resource allocation within the school. The research findings indicate that some school-effectiveness variables--including principals' instructional leadership and high expectations, time factors, and teachers' positive reinforcement--correlate highly with student achievement, while other variables are less closely related to achievement. (RW)