Experimental studies based on diagnostic prescriptive instruction, as it affects science achievement of college, high school, and middle school students, were analyzed statistically by the procedure of meta-analysis to determine the effectiveness of this instructional treatment. "Effect size" was calculated on each of 30 dependent variables. Data were organized by categorizing all treatments into one of three types: (1) Control, no diagnosis and no prescription; (2) Treatment I, diagnosis and no prescription; and (3) Treatment II, diagnosis and prescription or remediation. This yielded a total of 21 Treatment I and 32 Treatment II effect sizes. A mean effect size was then calculated for each treatment. Results of meta-analysis indicate that diagnostic prescriptive instruction significantly and positively influences science achievement. However, there is no clear indication that the use of prescription or remediation in addition to diagnosis brings about a significant increase in achievement. (Author/CS)