This meta-analysis reports the most comprehensive assessment to date of the strength of the relationships between the Big Five personality traits and academic performance by synthesizing 267 independent samples (N = 413,074) in 228 unique studies. It also examined the incremental validity of personality traits above and beyond cognitive ability in predicting academic performance.The combined effect of cognitive ability and personality traits explained 27.8% of the variance in academic performance. Cognitive ability was the most important predictor with a relative importance of 64%. Conscientiousness emerged as a strong and robust predictor of performance, even when controlling for cognitive ability, and accounted for 28% of the explained variance in academic performance. A significant moderating effect of education level was observed. The relationship of academic performance with openness, extraversion, and agreeableness demonstrated significantly larger effect sizes at the elementary/middle school level compared to the subsequent levels. Openness, despite its weak overall relative importance, was found to be an important determinant of student performance in the early years of school.These findings reaffirm the critical role of personality traits in explaining academic performance through the most comprehensive assessment yet of these relationships.