This systematic review explores the integration of STEM (Science, Technology, Engineering, Mathematics) and project-based learning (PJBL), analyzing 265 relevant papers to highlight their effects on self-efficacy, scientific reasoning, and learning achievement among high school students. It finds that while existing research indicates significant benefits of STEM and PJBL, there remains a lack of thorough integration within educational settings, presenting opportunities for further investigation. The study emphasizes the importance of these educational approaches in preparing students for 21st-century challenges and enhancing their skills for future careers.