Project-based learning (PjBL) has become a popular teaching method for 21st-century learning; however, academic performance improvement is a challenge. This study proposes a framework for designing personalized project-based learning (P-PjBL) experiences. To evaluate the effectiveness of P-PjBL, this study was conducted in two stages. In the first stage, a two-tier diagnostic test was developed using data from over 1,000 students. Subsequently, students' prior knowledge and understanding were assessed through the diagnostic test, and personalized activities and resources were created based on the test results. In the second stage, 106 fourth-grade students were divided into three groups and participated in a three-period unit. Control Group 1 followed traditional teaching methods, Control Group 2 engaged in general project-based learning (GPjBL), and the Experimental Group used P-PjBL. The results indicated that P-PjBL can effectively improve academic performance and reduce the student performance gap. Notably, P-PjBL had a more positive effect on students with moderate prior knowledge than those with limited prior knowledge. Moreover, students with higher-level prior knowledge demonstrated greater improvement in P-PjBL than those with low-level prior knowledge. These findings provide valuable insight into the potential benefits of P-PjBL for improving academic performance.