<![CDATA[This study examined the improvement of junior high school students’ mathematical problem-solving ability after the implementation of the Project Based Learning (PjBL) model. The research used a quantitative pre-experimental approach with a One-Group Pretest-Posttest Design. The population comprised all eighth-grade students of SMP Negeri 9 Langsa in the second semester of the 2025/2026 academic year. A purposive sampling technique was used to select class VIII-1, consisting of 29 students. Data were collected through essay tests administered before and after the treatment, supported by learning worksheets and an instructional module. The instrument was examined through validity, reliability, item discrimination, and difficulty analyses before being used in the study. The descriptive results showed an increase in the average score from 43.17 on the pretest to 73.66 on the posttest. The paired-samples t-test indicated a statistically significant difference between the two measurements (t(28) = 23.36, p < 0.001). These findings indicate that the implementation of PjBL was associated with a significant improvement in students’ mathematical problem-solving ability on the topic of measures of central tendency. The findings support the use of project-oriented learning as an alternative instructional model for mathematics learning that requires students to investigate, discuss, apply concepts, and formulate solutions to contextual problems.]]>
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