Challenges particular to second-year students have been identified that can impact persistence in science, technology, engineering, and mathematics (STEM) fields. We implemented a program to improve student success in intermediate-level science courses by helping students to feel they belonged and could succeed in STEM. We used survey measures of perceptions and attitudes and then qualitative measures to characterize the impact of support strategies, including peer mentoring, a second-year science student retreat, learning and advising support resources, and department-specific activities. Analysis of registration and transcript information revealed underperformance by students of color (SOC) and first-generation (FG) students in 200-level science courses. Comparison of these data before and during programming revealed significant improvement in success rates of these students in 200-level biology and chemistry courses, but success rates of SOC and FG students remain lower than the overall rate for 200-level science courses. Contemporaneous with the program, qualitative and quantitative measures of student attitudes revealed a high level of belongingness and support. The results suggest that a focus on students' metacognition about their own abilities and strategic knowledge of how to succeed may be a fruitful direction for future research.