<![CDATA[Students’ mathematical critical thinking skills in Indonesia remain relatively low, as reflected in the results of the 2018 PISA assessment. One of the main contributing factors is conventional teacher-centered learning. This study aims to describe the improvement of students’ critical thinking skills on the topic of three-dimensional shapes (cubes and rectangular prisms) through the implementation of the Project Based Learning (PjBL) model in Grade V of SD Negeri 01 Mamben Daya. This research is a Classroom Action Research (CAR) based on the Kemmis & Taggart model, conducted in two cycles. The research subjects consisted of 32 students (21 males and 11 females). Data were collected through a written essay test comprising five questions designed to measure indicators of interpretation, analysis, evaluation, and inference. Data analysis employed descriptive percentage techniques. The results showed a significant improvement. In the pre-cycle stage, the percentage of classical mastery of students’ critical thinking skills was only 3.12% (categorized as low). After implementing PjBL in Cycle I, the percentage increased to 56.25% (categorized as moderately critical). In Cycle II, it further increased to 78.12% (categorized as critical), exceeding the predetermined success indicator (?75%). The implementation of the Project Based Learning (PjBL) model is effective in improving the critical thinking skills of Grade V students on the concept of three-dimensional shapes. This study is recommended as an alternative instructional model to enhance the quality of mathematics learning in elementary schools.]]>
