Persistent concerns about the theory-practice gap and desires for an ‘evidence-informed’ teaching profession have prompted research into how teachers' epistemic beliefs influence their acceptance or rejection of educational research. This study analyses longitudinal interview data from six pre-service teachers (PSTs) to explore how experiences of conducting research (in the domains of science or education) during initial teacher education (ITE) contribute to epistemological development. These research experiences provided opportunities for ad-hoc epistemological development, even in the absence of intentional efforts. Epistemic beliefs sometimes appeared to be supplanted, counterproductively, from science to education. The implications for teacher education and research are discussed. •Pre-service teachers (PSTs) engaged in a yearlong research project in science or Education Studies.•Though some PSTs showed epistemological development, these appeared to be ad-hoc rather than intentionally planned.•Development in one discipline did not appear to necessitate development in the other.•PSTs need support in epistemological development and navigating epistemic boundaries between different disciplines.•Key considerations are raised for teacher educators integrating research experiences in Initial Teacher Education (ITE).