This research was aimed at improving students' democratic attitude and Mathematics learning achievement of measuring angle material using STAD cooperative learning method supported by angle-clock props. The subjects of this research were all 22 grade IV B students. This was a Classroom Action Research with two cycles. The research instruments used here were democratic attitude questionnaires, evaluation sheets, teacher's activity observation sheets, student's activity observation sheets, and democratic attitude observation sheets. The results showed that in cycle I, the average value of democratic attitude was 3.05. It improved on the cycle II with an average value of 3.52. This improvement was in line with the observations of student's democratic attitude with a score of 72.5% in cycle I and 81% in cycle II. It meant that the students' democratic attitude was very good during the learning process. Subsequently, students' learning achievement also increased. The average score of the learning achievement in cycle I was 67.72 with the percentage of completeness as much as 68.18%. In cycle II, it was 75.90 with the percentage of completeness as much as 81.81%. Those results reveal that the implementation of STAD cooperative learning method supported by angle-clock props can improve the democratic attitude and Mathematics learning achievement of grade IV B students of SD Muhammadiyah Purwokerto.