PENGARUH MODEL CASE-BASED LEARNING (CBL) TERHADAP PENINGKATAN KEMAMPUAN PEMECAHAN MASALAH MATEMATIS SISWA SMPNURLIFNARAMADANauthorABSTRACT Nurlifna Ramadan (2225200024). The Effect of Case-Based Learning (CBL) on Improving Mathematical Problem-Solving Skills in Junior High School Students. Thesis. Departemen of Mathematics. Faculty of Teacher Training and Education. Universitas Sultan Ageng Tirtayasa. Serang. 2025 Mathematical problem-solving ability is essential for student success, yet junior high school students demonstrate inadequate proficiency. This research investigates the Case-Based Learning (CBL) model's influence on mathematical problem-solving ability. A quasi-experimental design with nonequivalent pretest-posttest control group methodology was employed. The population included 60 ninth-grade students from SMPN 1 Sindangresmi, with purposive sampling selecting 60 students (n=30 per group). The instrumen was a four-item essay test assessing problem identification, strategy formulation, implementation, and solution verification. Data analysis used descriptive statistiks, Kolmogorov-Smirnov normality testing, Levene's homogeneity testing, and independent samples t-tests at p=0.05. Results showed the experimental group achieved significantly superior posttest performance (M=73.97) versus control group (M=66.67), p=0.036. Normalized gain analysis revealed significantly greater learning improvement in the experimental group (M=0.7646) versus control group (M=0.7000), p=0.013. Thus, this study concludes that the CBL model has an effect on improving the mathematical problem-solving abilities of junior high school students compared to conventional learning. Case-based learning, Problem Solving Ability,Conventional.L Education (General)Q Science (General)QA Mathematics2026UNIVERSITAS SULTAN AGENG TIRTAYASA;PENDIDIKAN MATEMATIKAThesis