This paper examines the research on how student-to-instructor ratio effects influence schooling, with particular attention to how the research relates to low-achieving children. It also summarizes the conclusions of several existing reviews of literature on: the effects on schooling outcomes of class or instructional group size; and scheduled, instructional, or engagement time. Findings include the following: (1) Reduced class size appeared to be most efficacious with low-ability or disadvantaged students when reductions were in the range typically associated with programs administered under Chapter 1 of the Education Consolidation and Improvement Act of 1981. (2) Such reductions can lead to better student and teacher attitudes and morale and to an enrichment of the core curriculum. (3) Increases in allocated, instructional, and engaged time lead to increases in learning. (4) Allocated time shows a lesser relation to achievement than more proximal time measures. (5) The greater amount of allocated time given to Chapter 1 students may serve to lessen an advantage that more able students possess because they generally spend more time engaged in appropriate tasks. (6) Reductions in class size and increases in time can only produce positive effects if the following also is true: teachers are adaptable and have the skills and motivation to capitalize on these instructions; the material taught and tested fits together; and the strategy for accomplishing the reduced student-instructor ratio creates fewer barriers to learning than it breaks down. A list of reference is appended. (PS)