This study investigates the influence of problem-based learning (PBL) on junior high school students’ engagement, motivation, and academic performance, with the aim of finalizing a standardized mathematics enrichment module. A quasi-experimental design was employed with two randomly selected groups: the control group (n = 42) received traditional mathematics instruction, while the experimental group (n = 42) participated in PBL-based enrichment classes over eight weeks. Data collection utilized adopted and validated instruments and proceeded in three phases: pre-test, PBL implementation, and post-test, with strict adherence to the university’s research ethics standards. Descriptive and inferential statistics were employed to address the study objectives. Findings reveal that students exposed to PBL demonstrated significant improvement in academic performance (p = .001, Cohen’s d = 0.624), whereas the control group exhibited a significant decline (p = .001, Cohen’s d = 0.800). The experimental group also reported high levels of engagement (M = 3.40) and motivation (M = 3.29), particularly in self-regulation and utility value. Pearson’s correlation analysis indicated a moderate positive relationship between engagement and motivation (r = 0.477, p = .001) and a weak but significant relationship between motivation and academic performance (r = 0.313, p = .044). These findings underscore the potential of PBL not only to improve academic outcomes but also to enhance motivation and engagement—critical affective components that support sustained learning. The results provide an evidence base for finalizing enrichment modules that incorporate authentic problem-solving, collaborative learning, and reflective activities. Embedding these features into standardized enrichment materials can help foster resilient, motivated, and high-performing mathematics learners in junior high school.