Effective science teaching methods can increase the learning process of learners. It facilitates both teachers and learners in creating an environment of learning. Therefore, the researchers tried to find the effect of a cooperative learning approach on student's achievement in the subject of chemistry. The main objectives of the study were: a) to study the difference between cooperative learning and traditional methodologies in terms of achievement in chemistry teaching at grade-IX and b) to analyze the difference between both methodologies in terms of achievement while comparing students of diverse intelligence of both groups. To accomplish these targets null hypotheses were tested. The nature of this study was experimental (Pre-test, Post-test equivalent group design). Forty-Two students were selected as a sample from Government Boys High School No 1 Nowshera Kalan on basis of pre-test score. Then two equal groups were formed i.e. experimental and control having an equal number of students 21 each. Both groups were taught the same three lessons, selected from of 9th-grade chemistry book (Khyber Pakhtunkhwa, Text-Book board). The Control group was taught these three selected lessons through the traditional method of science teaching. On the other hand, some chapters were taught to the experimental group through Slavin's student's team achievement division (STAD). This treatment lasts for six weeks and in the end, a teacher-made post-test was administered to both groups. The collected data were analyzed by applying an independent sample t-test. It was concluded from the analysis of data that chemistry learning through STAD was more effective than the traditional method of science. The same was also noticed for low achievers and high achievers of both groups. Based on the conclusion, it is recommended that science teachers should implement this method in their classrooms. Furthermore, curriculum developers should design such a curriculum which will be in favor of teaching this method.