Introductory science, math, and engineering courses often have problems related to student engagement, achievement, and course completion. To begin examining these issues in greater depth, this pilot study compared student engagement, achievement, and course completion in a small and large section of an introductory biology class. Results based on t-tests indicate that students in the small section of the course were more engaged and had higher achievement scores than students in the large section. Additionally, students in the small section were more likely to complete the course than students in the large section. Although further research is needed, reduced class size has the potential to be an effective strategy for improving student engagement, achievement, and course completion in an introductory biology course that has too often been a gatekeeper instead of a gateway for students who intend to be science, technology, engineering, and math majors.