This article describes a project designed to ensure that class participation in a large introductory commercial law course is assessed fairly and reliably. The subjectivity often associated with this type of assessment is minimized by involving students in the specification of clear criteria and the assessment process as they were asked to assess themselves and their peers. Formative feedback is given mid-way through the semester so that students have the opportunity to take remedial measures where necessary and teachers can reinforce positive behaviour. The data are analyzed to determine the relationships between the assessments given by the students, their peers and tutors. There is evidence of some gender bias in Week 13 that is not consistent with the final marks. Finally, the combining of the individual assessment of the criteria is shown to be a good estimate of the final class participation mark given by the tutors and the students.