Peer assessment involves students taking responsibility for assessing the work of their peers against set assessment criteria. They can therefore be engaged in providing feedback to their peers (sometimes referred to as peer review), summative grades (moderated by you or your colleagues), or a combination of the two. It's a powerful way for your students to act as the 'assessor' and to gain an opportunity to better understand assessment criteria It can also transfer some ownership of the assessment process to them, thereby potentially increasing their motivation and engagement. In doing so, your students might be encouraged to learn more deeply, building up their understanding, rather than just their knowledge of the facts, as well as gaining an insight into their own approach to an assessment task in comparison to their peers. This makes peer assessment an important component of Assessment for Learning, rather than simply a means of measuring performance. You may find that peer assessment is particularly useful in aiding your students to develop judgement skills, critiquing abilities and self-awareness.
You can use peer assessment for assessing both individual efforts and contributions to group work across a wide variety of activities. You can design peer assessment to be done openly, encouraging comparison and discussion, or anonymously depending on the assessment task and context. The key point is for you to to ensure that the participants (both your students and your colleagues) understand the purpose of peer assessment and what is expected of them. Preparation and clear assessment criteria are essential to supporting 'good' peer assessment.
Case studies discussing the benefits and limitations of peer assessment can be found in a paper published by Manchester Metropolitan University, Can students assess students effectively? Some insights into peer assessment. by Dr Mark Langan and Dr Philip Wheater (Department of Environmental and Geographical Sciences).