To estimate the influence of positive reinforcement on classroom learning, the authors analyzed statistical data from 39 studies spanning the years 1958-1978 and containing a combined sample of 4,842 students in 202 classes. Twenty-nine characteristics of each study's sample, methodology, and reliability were coded to measure their effects on reinforcement and learning. The types of reinforcement tested ranged from intangible social approval to tangible (even edible) objects. Statistical analysis using regressions and analysis of variance showed that reinforced students have markedly higher learning outcomes than do non-reinforced control students. Contrary to previous theory and opinions, the strong effects of instructional reinforcement appear constant across grades (kindergarten through college), socioeconomic levels, race, private and public schools, and community types. Tangible reinforcements may be slightly more effective than intangible ones, and female and special-school students may be slightly more affected by reinforcements, but generally there is little strong evidence that some types of reinforcers are more effective than others. (Author/RW)