This paper reports on a research project exploring the aspirations, assumptions and experiences of students on a Master's in Education course. Professional Learning (PL) for teachers in England has increasingly prescribed content and delivery, is highly regulated and embedded within politically sanctioned evidence-based research, structured in linear, accelerated modes. This PL largely ignores the contested ideological spaces education inhabits, reducing opportunities for teachers to engage in situated, relational, exploratory work towards how, why or for whom educational values and practices are enacted. The data suggests that liminal PL spaces are characterised by fluidity and uncertainty, often productive of personal and professional change. Using one Master's in Education course as an assemblage of liminal PL, where curriculum design and critical pedagogic approaches foreground socio-material and affective conditions, we argue that liminality can generate creative, critical, and agentic responses to knotty issues of education. We argue that liminal PL spaces need rigorous defending as shifts to regulated PL (e.g. the Early Career Framework in England) grow apace. Drawing on focus groups (n = 4 + 50), we pay attention to what teachers say mattered in their personal/professional learning. Our findings foreground non-linear, multiple ways of becoming teacher, and we further reflect upon affordances of liminal PL spaces.