Here are a few of the articles I looked at and what they said:
Cho, K., Schunn, C. D., & Wilson, R. W. (2006). Validity and Reliability of Scaffolded Peer Assessment of Writing from Instructor and Student Perspectives. Journal of Educational Psychology, 98(4ov), 891.
Students and instructors do not trust peer-grading schemes, however, there is high reliability and validity in these schemes if done correctly.
Instructors often have no time to grade and therefore skim through assignments while peer graders will take time on each assignment, judging its quality more in depth
Instructors grade papers with no other help, while peer graders will usually grade multiple papers, giving each paper a combined rating from multiple peers. Bias can be reduced with this method.
Studies in the past have either predicted high or low validity in peer grading, they produced mixed results, some because of errors.
Even when peer grade validity is high, students may not perceive it as such.
Self assessments are generally less accurate than peer assessments and are often more influenced by self-esteem than actual performance. This is one of the reasons students often feel that peer-assessments are not accurate.
Multiple peers should be used to rate each other
What an instructor views as reliable peer assessment is usually different than what a student views as the same.
Overall, peer assessment may be more valid than instructor assessment because multiple people are rating a single work, instead of a single person rating a single work.
Peer review is part of student's learning process.
Concerns about reliability and validity are not valid reasons to shy away from peer assessment.
Lejk, M. & Wyvill, M. (2001b) The effect of the inclusion of self-assessment with peer assessment of contributions to a group project: a quantitative study of secret and agreed assessments, Assessment and Evaluation in Higher Education, 26(6), 551–561.
Peer assessment is better done without self assessment
Magin, D. J. (2001) A novel technique for comparing the reliability of multiple peer assessments with that of single teacher assessments of group process work, Assessment and Evaluation in Higher Education, 26(2), 139–152.
Group members are generally more able to assess each other than mentors or teachers
Struyven, K., Dochy, F., & Janssens, S. (2008). The Effects of Hands-On Experience on Students' Preferences for Assessment Methods. Journal of Teacher Education, 59(1), 69.
Teachers and student teachers generally react negatively to forms of assessment that they are not used to
Traditional assessment methods were often negatively looked upon by students and alternative methods were perceived to enable quality learning
Kilic, G. B., & Cakan, M. (2007). Peer Assessment of Elementary Science Teaching Skills. Journal of Science Teacher Education, 18(1), 91.
Peer scores significantly correlate with instructor scores
Ryan, G. J., Marshall, L. L., Porter, K., & Jia, H. (2007). Peer, Professor and Self-Evaluation of Class Participation. Active Learning in Higher Education: The Journal of the Institute for Learning and Teaching, 8(1), 49.
One study with 144 students in higher ed led to a 0.83-0.9 correlation coefficient between instructor and student ratings with forced distribution
Another similar study with another 144 students led to a correlation of 0.72 between instructor and student ratings.
This study found that rankings were statistically different but not academically different (not enough to affect a student's grade).
Problems arising from group grades include “inflated grading of friends, lack of discrimination among members of a group, individuals dominating to seek higher marks, and students who do less work but still benefit from a group grade.” forced distribution or ranking reduces all of these problems to some degree.
Students did not like this type of grading overall.
Forced distribution (ranking) of each other's grades affected whether students gave a higher or lower grade to their peers.
Peer assessment should be scaffolded
Wen, M. L., & Tsai, C. (2006). University Students' Perceptions of and Attitudes toward (Online) Peer Assessment. Higher Education: The International Journal of Higher Education and Educational Planning, 51(1), 27.
Peer assessment can increase student-student interaction, enhance students understanding of other student's ideas, increase learner's understanding in the cognitive and meta-cognitive domains, and develop transferable and social skills
Peer assessment methods should make criteria clear to students
Anonymous assessment may produce better validity of assessments
A study with 280 college students found that most felt it appropriate to use peer assessment as a small portion of their grade
Students had a positive attitude toward peer assessment
Results suggest that “more effort needs to be placed on giving students responsibilities for grading, to develop a sense of learner control and ownership of their own learning, especially in higher education.”