This paper uses cultural historical activity theory to examine the interactions between the choices primary teachers make in the use of practical activities in their teaching of science and the purposes they attribute to these; their emotions, background and beliefs; and the construction of their identities as teachers of science. It draws on four case studies of science lessons taught over a term by four exemplary teachers of primary science. The data collected includes video recordings of science lessons, interviews with each teacher and some of their students, student work, teachers' planning documents and observation notes. In this paper, we examine the reflexive relationship between emotion and identity, and the teachers' objectives for their students' learning; the purposes (scientific and social) the teachers attributed to practical activities; and the ways in which the teachers incorporated practical activities into their lessons. The findings suggest that it is not enough to address content knowledge, pedagogy and pedagogical content knowledge in teacher education, but that efforts also need to be made to influence prospective primary teachers' identities as scientific thinkers and their emotional commitment to their students' learning of science.