As we know meta-analysis has recently been suggested as an important tool and a quantitative technique for the combination and comparison of different but similar studies. The purpose of meta- analysis is to synthesis results provided by multiple studies to observe effect sizes across the studies on the variables under review with the aim of going a greater understanding of related research reports.

In this study we are looking for the ways in which we reach more reliable and more accurate estimations after assessment by one test in each study.to follow this aim we consider different methods of meta-analysis to synthesis data obtained from a series of assessments.

Studies included were 42 separate experimental studies where in two-group experimental design was used to study the effectiveness of instructional programs on creativity. The Torrance Tests of Creative Thinking was the main instrument in all the studies. Then a data set was derived from the studies and analysed with two different methods of meta – analysis namely Hunter& Schmidt technique and Glass technique.

Findings showed that, firstly method of Hunter& Schmidt is better than the Glass technique in our interested area. Second, the evidence presented in this study suggested that, in general, creativity can be enhanced to a high degree through instructional program in terms of how powerful are calculated effect sizes based on Cohen’s table.

To sum up, it can be concluding that the ability of meta-analysis to produce concise and easily interpretable findings makes a significant contribution to educational and psychological assessment. It has been found true to be when we have done a series of tests or assessments in one area.