Effective teaching and learning of science depends on the selected teaching method touching students' most learning senses. This study investigated the effects of cooperative learning on eighth grade students' achievement and attitude toward science. Participants were 68 students from two different eighth grade classrooms in an elementary school. The classrooms were selected randomly as the experimental group and the control group. In the experimental group cooperative learning was employed, while in the control group direct instruction took place in order to teach the unit "Reproduction and Development of Living Organisms." The experiment was completed within a five-week period. In order to assess the treatment effects on the students, Science Achievement Scale (SAS) and Attitude Scale toward Science (ASTS) were administered as pre- and post-tests to both groups. The results of t-tests demonstrated that the students in the experimental group had better performance on post-SAS and post-ASTS scores. (Contains 2 figures and 4 tables.)