The present study examined the extent to which the relationships between student self-reported math grades and different types of student variables (standardized math test scores, interest and effort in math, parental education) are predicted by classroom composition and teachers' classroom management. Based on a representative sample of 31,038 8th-grade students from 1,470 classrooms, multilevel regression analyses revealed that grades were less strongly related to students' test scores and more strongly related to students' effort in classrooms with an unfavorable academic composition (i.e., low average test performance). Classroom management was found to moderate the association between academic classroom composition and the parental education-grade relationship, indicating a noticeable grade advantage of students with high parental education in classrooms with both an unfavorable academic composition and ineffective classroom management. Our findings highlight the relevance of classroom composition and classroom management to research on teachers' grading and point toward possible ways to improve current grading practices.