Models of research use in education tend to focus on specific elements of education systems or underplay the complexity of system change. Within other public policy areas, notably health, more work has been undertaken to integrate systems thinking when considering knowledge mobilisation and research use. In this paper, we survey public policy system change literature to develop a set of system dimensions. We use these to examine models relating to research use that are widely referenced in education. We then apply these dimensions to the work of the Education Endowment Foundation (EEF), the UK's What Works Centre for Education, which aims to support evidence-informed practice at all levels of the education system. We focus on its work to embed research-informed practices in regional school systems, through a case analysis of two 'scale-up campaigns' to mobilise evidence relating to the effective deployment of teaching assistants (educational support paraprofessionals). The findings highlight the value of using the system dimensions framework as a diagnostic tool to understand how to effect system change, highlighting the key role of brokerage and system leadership at different system levels; school-level capacity to implement change; and system relationships.