Integration of active-learning approaches into increased-structure postsecondary classrooms significantly improves student academic outcomes. We describe here two parallel sections of Introductory Biology that shared learning objectives and content but varied in course structure. The large-enrollment traditional course consisted of four 50-minute lectures coupled with minimal active-learning techniques, while an increased-structure intervention course integrated multiple active-learning approaches, had limited enrollment, and comprised three 50-minute lectures combined with a fourth peer-led team-learning discussion section. Additionally, the intervention course employed weekly review quizzes and multiple in-class formative assessments. The academic impact of these two course formats was evaluated by use of common exam questions, final grade, and student retention. We showed that academic achievement and retention of participants enrolled in the intervention course was significantly improved when compared with the traditional section. Further, we explored whether promoting in-class student-student/student-instructor interactions and peer-led discussion sections fostered a greater sense of belonging. At the end of the course, participants in the intervention course reported greater perceptions of classroom belonging. Therefore, this study begins to characterize the importance of combining pedagogical methods that promote both academic success and belonging to effectively improve retention in science, technology, engineering, and mathematics majors.