In Sweden, systematic reviews have prompted a strong government focus on implementing formative assessment in science and mathematics education. However, the intention behind this investment—to improve Sweden’s position in TIMSS and PISA appears to overlook the difficulty of putting research into practice. The purpose of this study is to explore the problems associated with incorporating formative assessment into classroom work by focusing on the experiences of a physics teacher who participated in a local development project in an upper secondary school in Sweden. The case study is based on a phenomenological approach which emphasises collaboration between researcher and participant, and five different themes of lived experience are described as a result of joint interpretations: (1) resistance from the students; (2) stuck in formal teacher roles; (3) sacrifices to bring about change; (4) avoiding risks in the classroom; and (5) worries about the opinion of others. These lived-through dimensions deepen our understanding of the barriers which some teachers face and carry implications for the support they need. Finally, this article points out the challenge for the systematic review movement in Sweden, and elsewhere, to incorporate and communicate the different strands of research on formative assessment.