Background/purpose: This study investigates the effectiveness of Problem-Based Learning (PBL) integrated with scaffolding in enhancing problem-solving skills among students with varying levels of prior knowledge. The main objective is to determine how scaffolding, when combined with PBL, can support students in developing stronger problem-solving capabilities across diverse cognitive baselines (prior knowledge levels). Materials/methods: A quasi-experimental 2x3 factorial design was employed, involving 172 students divided into experimental and control groups, each stratified by prior knowledge (low, medium, high). The experimental group received PBL instruction enriched with scaffolding tools, such as concept maps, diagrams, and structured tables, while the control group followed standard PBL without additional aids. Pretests and posttests were administered to assess four key indicators of problem-solving skills: understanding the problem, planning, implementation, and review. Data were analyzed using the Kruskal-Wallis test followed by Dunn-Bonferroni post-hoc comparisons. Results: The findings demonstrated that students in the experimental group significantly outperformed their control counterparts across all indicators. Scaffolding showed a stronger impact on students with low and medium prior knowledge, enhancing their ability to manage cognitive load and apply systematic problem-solving strategies. Conclusion: The integration of scaffolding within the PBL framework substantially improves students' problem-solving skills, especially in heterogeneous classrooms. This approach offers a practical model for differentiated instruction that meets the needs of students across diverse prior knowledge levels.