Educators in higher education commonly use peer and self evaluations to help assess student performance on group projects. Although these evaluations provide multiple benefits, many educators are wary of using them due to concerns about their quality. This study addresses three questions debated in the literature regarding the quality of these assessments. How much do students differentiate among peer contributions through their ratings? How reliable are peer ratings? How much agreement exists between peer and self ratings? Although these questions have been addressed to varying degrees in past work, their answers have been far from settled. While many studies focus on just one of the questions, this study's data make it possible to address all three questions for the same group of students as well as examine each question by student performance level. The evaluations assessed in this study were completed by a large number of students under conditions associated with obtaining more valid and reliable ratings. Overall, the results provide support for using peer and self evaluations to help assess student contributions to group projects. Peer ratings were largely reliable as group members generally agreed on the scores given to their peers. In addition, most students differentiated among group member contributions through their ratings. Students also tended to rate themselves higher than their peers rated them. This study has implications for how peer and self evaluations can be most effectively used by educators to measure student performance in group work.