There is a widespread conviction in research on teacher education that practicum contributes to the development of student teachers' inner qualities. This article presents a systematic review of empirical research articles on teacher affect, identities, and conceptions of mathematics, based on 87 publications from 2001-2021. Becoming a teacher is described as a slow, uncertain, and individual process, with varied assumptions about what or whom the prospective teacher needs to become or feel. Generally, a synthesis was difficult, partly due to contextual as well as methodological differences among the included articles. Still, we could conclude how tensions between identities endorsed by school and university became influential for identity development. For affect, we saw contradictory results in how positive attitudes to mathematics can increase or decrease after practicum, and in how stable they are. Studies disagreed on the extent to which students' attitudes and beliefs determine their teaching approach. Despite this complexity, practicum-as-usual appears less successful than various interventions. This may have to do with the widespread implementation fidelity perspective, or with aspects focused on interventions being made more accessible for participants.