Learning is a social event and so the students need learning environments that enable them to work with their peers so that they can learn through their interactions. This study discusses the effectiveness of cooperative learning compared to traditional instruction in terms of students' motivation and understanding of chemical kinetics in a high school chemistry course. Participants were 110 eleventh grade students from two different schools. The researchers administered the Reaction Rate Concept Test to measure the students' understanding of chemical kinetics, the Science Process Skill Test to decide whether the groups were different in terms of their science process skills before instruction, and the Motivated Strategies for Learning Questionnaire to assess students' motivation for a chemistry course. Results of the experiment showed that compared to traditional instruction, cooperative learning enabled better understanding of the concepts of chemical kinetics and improved students' motivation to study chemistry for both schools. (Contains 7 tables and 2 figures.)