<![CDATA[Mathematics learning at the elementary level requires instructional approaches that promote conceptual understanding, active participation, and problem-solving abilities. However, students may experience difficulties understanding two-dimensional shapes when learning activities rely primarily on teacher explanations and individual exercises. This study aims to examine the implementation of the collaborative-based Student Teams Achievement Divisions (STAD) cooperative learning model in improving mathematics learning outcomes and strengthening student collaboration in learning two-dimensional shapes. The study employs a convergent mixed-methods approach, combining quantitative data from learning outcome tests and questionnaires with qualitative data obtained through classroom observations, interviews, and documentation. The findings highlight the role of heterogeneous group formation, peer discussions, idea exchange, shared problem-solving, and individual assessments in supporting students' mathematical learning experiences. The implementation also provides opportunities to develop communication, teamwork, and individual responsibility. The study emphasizes that integrating collaborative engagement with individual accountability is important for creating meaningful mathematics instruction. The implications suggest that teachers should organize structured cooperative learning activities that balance peer interaction and individual assessment to support conceptual understanding and improve the quality of elementary mathematics education.]]>
