This study is a meta-analysis of the question “What are the effects on achievement of different teaching techniques?” Twelve categories of teaching techniques were specified. Among these are questioning, wait-time, testing, focusing, manipulative, presentation approach, inquiry or discovery, audio-visual, and teacher direction. A coding form was then developed to allow for the uniform examination and recording of 76 variables from each study. One or more effect sizes were calculated and coded for each study. Over 300 microfilmed dissertations covering the past 30 years were examined. Some 2000 ERIC science abstracts were reviewed and suitable studies obtained. Finally, journal articles were reviewed. A total of 400 effect sizes representing 160 studies were produced. The main effect size overall was 0.34. Thus, for all samples considered the experimental science teaching techniques on the average resulted in one-third of a standard deviation improvement over traditional techniques. Mean effect sizes also were calculated for each technique. More than 20 other variables such as class size, community type, and science subject area were cross-tabulated with effect size.