Shelf help: what powers medical student subject exam performance in the United States

Following the change in 2022 of a scored United States Medical Licensing Examination (USMLE) Step 1 to a binary pass-fail grading system, greater emphasis has been placed on the Step 2 Clinical Knowledge (Step 2 CK) exam. Shelf or subject exams offered by the National Board of Medical Examiners (NBME) help prepare students for Step 2CK and therefore deserve the attention of clerkship directors. This paper reviews the literature pertaining to the factors that positively and negatively impact medical students' performance on the shelf exams, including but not limited to performance in the pre-clinical years, clinical exposures, peer learning, active or team-based learning, length of clerkships, and order and number of previous shelf exams.

The PubMed database was searched to identify studies describing factors influencing performance on shelf exam scores during medical school and strategies for improving shelf scores. Studies were identified through iterative searches using multiple keyword combinations related to NBME shelf examinations, NBME subject examinations, clerkship performance, academic achievement, and educational interventions. Inclusion criteria consisted of English-language studies published between 2005 and 2025 involving students at U.S. allopathic or osteopathic medical schools. The included studies were reviewed for relevance and methodological rigour, including consideration of study design, sample size, statistical analyses, and reported outcomes.

A robust pre-clinical education remains vital for success on NBME shelf examinations. Exam scores are also influenced by the number and order of previous exams. Increased clinical exposure, active learning, team-based approaches, and peer review sessions have not consistently shown improvements in performance.

This review underscores the importance of a foundational understanding of the basic sciences for student success on exams, while acknowledging that clerkship directors must balance their obligation to adequately prepare students for standardized testing with their mission to craft compassionate and competent future clinicians.