Medical school accreditation and educational outcomes: a national equity study of students’ university grades and comprehensive exam scores

National medical school accreditation is intended to differentiate institutional quality and support improvement. However, there is limited country-specific evidence on whether accreditation categories align with measurable student outcomes. This study examines the association between accreditation category and years of accreditation with internal university grades and performance on the Comprehensive Basic Science Examination (CBSE), and explores gender differences. A nationwide retrospective study examined CBSE results from 2019 to 2021. Universities were categorized by the duration of their national accreditation: long-term, mid-term, or short-term. CBSE scores, grade point average (GPA), and repeat examination results were documented as outcomes. Performance differences in CBSE, GPA, and repeat rates were evaluated across accreditation categories and gender. A total of 25,757 individuals from 23 medical schools were included in the study. Female students outperformed males in university courses, while males scored significantly higher in CBSE (both P < 0.001). CBSE scores varied by accreditation status, with higher mean scores in long-term accredited universities than in mid- and short-term accredited institutions ( P < 0.001). Conversely, GPA was elevated in short-term accredited institutions, indicating a diminished alignment between internal assessments and standardized performance. Short-term accredited universities exhibited higher repeat-examination rates ( P < 0.001). Accreditation category and years of accreditation are associated with higher CBSE performance and more favorable repeat-testing patterns, while internal grading shows an inverse pattern. These findings suggest that standardized examination outcomes may align more closely with accreditation tiers than institutional grades, and they highlight the need to strengthen governance and comparability of internal assessment across institutions.