This article presents the results of an action research project that focused on giving students more sense of control and responsibility over their own learning by engaging them more fully in assessment and helping them to understand the principles underpinning assessment criteria. The course is a second-year music module with approximately 85 students. I formed the class into groups to grade model answers and compiled a list of what they believed the assessment criteria should be based on this experience. I then used this list to compile a self-assessment criteria sheet, which the students filled out themselves and attached with each subsequent assessment. When I completed my analysis of data from the first cycle of action research, I implemented the learning from that cycle into a second and third cycle of action. This involved re-evaluating my initial plans in light of my findings; building on what was successful and changing what was not, and refocusing my research. The findings were significant, as their assessment results improved dramatically. Involving students throughout the assessment process, from initially setting the criteria right through to self-assessing their work, improved their grades, reduced student passivity and increased their self-confidence. (Contains 3 notes.)