The "assessment 'for' learning" movement in education has increased attention to self-grading and peer-grading practices in primary and secondary schools. This research synthesis examined several questions pertaining to the use of self-grading and peer-grading in conjunction with criterion-referenced testing in 3rd- through 12th-grade-level classrooms. We investigated (a) the effects of students' participation in grading on subsequent test performance, (b) the difference between grades when assigned by students or teachers, and (c) the correlation between grades assigned by students and teachers. Students who engaged in self-grading performed better (g = 0.34) on subsequent tests than did students who did not. Moderator analyses suggested that the benefits of self-grading were estimated to be greater when the study controlled for group differences through random assignment. Students who engaged in peer-grading performed better on subsequent tests than did students who did not (g = 0.29). On average, students did not grade themselves or peers significantly differently than teachers (self-grades, g = 0.04; peer-grades, g = 0.04) and showed moderate correlation (self-grading, r = 0.67; peer-grading, r = 0.68) with teacher grades. Further, other moderator analyses and examination of studies suggested that self- and peer-grading practices can be implemented to positive effect in primary and secondary schools with the use of rubrics and training for students in a formative assessment environment. However, because of a limited number of studies, these mediating variables need more research to allow more conclusive findings.