<![CDATA[The low mathematics learning outcomes in the material of plane figures is still a problem faced by elementary school students. This condition is caused by learning that is still centered on the teacher so that students are less active in building conceptual understanding and solving problems. This study aims to improve mathematics learning outcomes in plane figures through the application of the Problem Based Learning (PBL) model to fourth-grade students of UPT SD Negeri 064990 Medan Johor. This study is a Classroom Action Research (CAR) that uses the Kemmis and McTaggart model with two cycles, each of which includes the planning stage, action implementation, observation, and reflection. The research subjects were 19 students in grade IV-C. Data collection techniques were carried out through observation, learning outcome tests, and documentation, while data were analyzed using quantitative and qualitative descriptive techniques. The results of the study indicate that the application of the Problem Based Learning model can significantly improve students' mathematics learning outcomes. The percentage of classical learning completion increased from 47.37% in the initial condition (pre-test) to 73.68% in Cycle I and reached 89.47% in Cycle II, with a class average score of 82.84, thus exceeding the research success indicator, which is at least 80% of students achieving a score above the Minimum Competency (KKM) of 72. Furthermore, teacher activity increased from 83.33% to 94.44%, while student activity increased from 75% to 91.67%. Thus, the implementation of the Problem-Based Learning model has proven effective in improving mathematics learning outcomes in plane geometry and encouraging active, collaborative, and student-centered learning.]]>
