Background: A two-step selection procedure, consisting of a non-academic and an academic step, was recently shown to select students with a 2.6 times lower risk of early dropout and a higher clerkship Grade Point Average (GPA) than lottery-admitted controls. Aim: To determine the relative contribution of the non-academic and academic steps to differences found in student performance. Method: Lottery-admitted students (n = 653) and three groups of selection procedure participants were compared on early dropout rate and clerkship GPA: (1) all participants (n = 1676), (2) participants who passed step 1, and (3) participants who passed step 2. Results: Selection procedure participation resulted in a 4.4% lower dropout rate than lottery admission and this difference increased to 5.2% after step 1 and to 8.7% after step 2. Clerkship GPA was significantly higher for participants who passed step 1 than for their lottery-admitted controls. This difference remained significant after the rejection of students on academic criteria in step 2. Conclusion: The lower dropout rate of selected students is related to both self-selection of participants before the start of the selection procedure and the academic part of the selection procedure. The higher clerkship GPA of selected students is almost exclusively related to the non-academic selection criteria.