This article considers the motivations of teachers to pursue ongoing professional learning. During recent decades, the international policy context has been characterised by high-stakes accountability, but the implications of this agenda for teachers' motivations toward professional learning remains under-explored. In this mixed methods study, combining a large teacher survey and in-depth teacher interviews, a new and significant concept of 'instrumental motivation' is generated to capture how high-stakes performance management policies damage the motivation of teachers to learn professionally. This innovative approach, employing ordinal factor analysis and inductive/deductive hybrid thematic analysis inclusive of self-determination theory, reveals how the 'instrumental motivation' of teachers should be constrained and argues for the adoption of alternative motivational strategies to support effective professional learning in schools.