Student involvement in assessment is considered essential to assessment for learning (AfL), mainly for developing a shared understanding of what it means to be a competent learner. However, translating AfL into practice has been difficult because teachers are reluctant to co-share assessment responsibilities with students. Thus, this paper explores secondary teachers' perceptions of student involvement in assessment and feedback from the angle of power relations and highlights the conflicting positions and challenges of inviting students into the decision-making process and negotiations on assessment. The data set was purposefully collected from three focus groups of teachers from three upper secondary schools in Iceland. The findings indicate that power relations influence teachers' perception of student involvement. Power relations are mediated by teachers' positions and their knowledge, language, and space. Moreover, the findings show that developing relationships of trust is critical in creating a space for dialogue and student involvement.