Grade 10 students in SMAK XYZ were not behaviorally, emotionally, and cognitively engaged in mathematics class. It could be seen through observation. Besides, it was confirmed by mentor and students’ questionnaire result that students were not engaged during the learning. They rarely asked question, preferred to talk to friends than listen to the teacher’s presentation, felt bored during the learning, and their mathematics grades were low. Thus, researcher implemented STAD learning method to increase students’ engagement in learning mathematics and to investigate how STAD learning method increases the student engagement. The method used in this research was Classroom Action Research. It used Kemmis and Taggart action research model that lasted in three cycles. It was conducted on October 1st - 20th, 2015 and involved 24 (14 males and 10 females) grade 10 students at SMAK XYZ. The used instruments were: mentor’s observation sheet for student engagement and implementation of STAD, mentor’s interview guideline, students’ questionnaire, quiz sheet, and researcher’s journal reflection. The data was analyzed by using statistic descriptive and qualitative descriptive. The result of those instruments was all of the indicators of student engagement had reached the cycle continuation criterion that was determined by researcher and improved from cycle I to cycle III. The instrument also showed that STAD learning method was done well during the research. As a conclusion, STAD learning method could increase the students’ engagement (behaviorally, emotionally, and cognitively) in learning mathematics as long as the steps of STAD learning method were implemented correctly.