A meta-analysis of research on college students in science, mathematics, engineering, and technology (SMET) was undertaken to clarify the effects of small-group learning at the undergraduate level. The focus was three broad categories of outcomes among SMET undergraduates: achievement, persistence, and attitudes. Research concerns included: potential sources of bias in the methodology; whether the effects of small-group learning differ for various groups of students (majors or nonmajors, first-year or other students, men or women, predominantly white or predominantly underrepresented groups); and whether the characteristics of different small-group learning procedures (time spent working in groups) are related to the outcome measures. Using 39 studies from 1980 or later, the study demonstrated that various forms of small-group learning are effective in promoting greater academic achievement, more favorable attitudes toward learning, and increased persistence. The magnitude of effects reported in this study exceeded most findings in comparable reviews of research on educational innovations and supports more widespread implementation of small-group learning in undergraduate SMET. Three figures and five data tables are appended. Also appended is a bibliography of the characteristics of various meta-analyses studies. (Contains 86 references.) (SW)