This paper reports the results of an investigation on the effect of cooperative learning on academic achievement of physics course. Cooperative learning was employed to experimental group and conventional teaching method was used for control group. Sampling of the study consists of 15-16 years old 220 students at high school in Iran. The progress and retention were determined by means of a self-developed "Physics course". A clear significant difference, as a conclusion, was detected in favor of the experimental group indicating the success of the cooperative learning. Further research is needed to explore the effects of cooperative learning on academic achievement. (Contains 2 tables.)