The aim of this study was to examine effectiveness of applying learning together (LT) method at different intervals on improvement of middle school students' academic success and science process skills. The sample of study consisted of 117 sixth and seventh grade students in two public middle schools. In this study, the "Solomon Experimental Design" was used. In the first year of the application was conducted with sixth grade students, and in the second year, a year later, the same students who graduated to the seventh grade and an additional seventh grade class who had not participated the year before were included in the study. The experimental groups were applied the LT method and control groups were applied the existing method which the middle school science curriculum followed in Turkey was taught. As data collection tools, Preliminary Information Tests, Science Process Skills Tests and Academic Achievement Tests were used. According to the findings, the Solomon Experimental Design, applied twice different intervals in the same group of students, internal and external validity of the research was increased. In conclusion, it was found that the two-time application of the LT in teaching a subject to the same students group was more effective than the one-time.