The purpose of this study is to determine the effect of learning together technique of cooperative Learning method on student mathematics achievement. The study was an experimental research in which pre-test -- post-test design with control group was applied. The study was conducted in spring 2004 with 70 pupils studying at 7th class in Balikesir, Turkey. In this study, experiment and control groups have been used. "Learning Together" technique of "Cooperative Learning" method has been applied to the experiment group and "Traditional Teaching" method has been applied to the control group. Before applying the measure means is given to groups as pre-test. In the end of applying is practised post-test to groups. Conclusions showed that there is a significant difference between the results of experiment and control groups. Learning Together technique of cooperative learning method is more effective than traditional teaching methods.