In this Information Age, mathematics learning has shifted from independent to collaborative, and the ability to utilize both intrapersonal and interpersonal skills in learning has become essential. To cultivate multiple intelligences in mathematics classrooms, integrating project-based learning into mathematics instruction can be a promising approach. In this study, we analyzed 15 elementary interns' project-based mathematics (PBM) lessons and observed their implementation at two public elementary schools in the southern United States. The findings revealed that the science, technology, engineering, and mathematics (STEM) PBM lessons conducted by the interns shared five common features: (a) enhancing empathy and social awareness, (b) solving real-life mathematics-related problems, (c) utilizing personal strengths to enhance the utility of mathematics, (d) supporting wide-ranging and collective mathematics learning, and (e) cultivating personal responsibility in mathematical problem solving. We further discussed how these STEM PBM lessons guaranteed an opportunity to foster students' social and emotional learning competencies in mathematics classrooms. We conclude that PBM provides a practical way to effectively engage students and enhance learning purpose in elementary classrooms and recommend this innovative pedagogy to both novice and veteran elementary teachers.