Medical schools with a diverse student body face the challenge of ensuring that all students succeed academically. Many medical schools have implemented prematriculation programs to prepare students from diverse backgrounds; however, evidence on their impact is largely lacking. In this study, we analyzed participants' demographics as well as the impact of the prematriculation program on Year 1 performance. Predictive validity of the program was assessed and compared to other traditional predictors, including grade point average (GPA) and Medical College Admission Test (MCAT) scores and subscores. Linear mixed effect models determined the impact of the prematriculation program, and linear regression analysis assessed the predictive value of the overall score in the prematriculation program and other traditional predictors. Demographics of students participating in the prematriculation program from 2013 to 2015 (n = 75) revealed a significantly higher prevalence of academically disadvantaged students including older students, students with lower GPA and MCAT scores and students of racial and ethnic populations that are underrepresented in medicine, compared to non-participants (n = 293). Participants performed significantly better in Year 1 courses that were covered in the prematriculation program compared to courses that were not covered. The overall performance in the prematriculation program correlated significantly with Year 1 performance and was found to be a strong predictor for Year 1 performance. This study suggests that a prematriculation program can help students to succeed in the first year of medical school. The results have implications for medical schools seeking to implement or evaluate the effectiveness of their prematriculation program.