Teachers’ assessment and grading of student achievement is often charged for not being reliable. Various suggestions of how to reach higher levels of reliability are advocated in different contexts, and one suggestion is “social moderation”. Social moderation involves teachers working together when assessing and grading student performance. Although the claim is often made that moderation practices lead to higher levels of reliability in teachers’ assessment and grading, such claims often lack scientific support. In this study, a literature review has been carried out in order to gain knowledge about the potential effects that moderation may have and whether these effects may in fact lead to more reliable assessment and grading. The results indicate that moderation practices do have an effect, which may ultimately lead to higher levels of reliability if these practices involve several levels in the assessment process. Moderation is also a process that can be affected by several factors, such as the organization of the moderation meetings and the selection of student performance.