The learning achievement level of class XD students at SMAN 1 Kurau in chemistry is still relatively low, as indicated by the low number of students who successfully achieved the completion criteria, which was only 25.93%. Active student participation during the learning process is also still minimal. The purpose of this study was to determine the effectiveness of the application of the method. Student Teams Achievement Division (STAD) in improving student learning outcomes to achieve the classical mastery target of 85%. This study uses a classroom action research approach conducted in class XD SMAN 1 Kurau, and is divided into two cycles. Each cycle includes the stages of planning, action implementation, observation, and reflection. Data collection techniques include tests, observations, and documentation, while data analysis is carried out quantitatively. From the results of the study, it can be concluded that the implementation of the STAD method has been proven to be able to improve students' chemistry learning outcomes in the class to reach the classical mastery standard of 85%.