National studies concerned with the assurance of students' language communication within higher education courses have identified several principles for leveraging change, which include an institutional wide strategy, the articulation of clear language communication outcomes at the course and subject level, the identification of subjects within courses from first year to the capstone that have a particular focus on teaching and assessing communication skills, the incorporation of English language and literacy into assessment criteria, and collaboration between discipline staff and academic language and learning staff (Arkoudis, 2012, 2014). These principles have been incorporated into an English Language Policy at one university; they require significant change in the way language education is perceived and practiced as a mainstream part of the higher education curriculum, pedagogy and assessment. This presentation showcases how a diagnostic process drawing on practice theory, and in particular Kemmis, et al's (2014) notion of practice architectures, can assist in making sense of how this kind of long-term sustainable change may be facilitated. To explain, Kemmis, et al (2014) remind us that changing practice is not merely a matter of communicating policy and offering professional development to individuals. Sustainable change to practice can only occur as a result of attending to the practice architectures - the cultural-discursive, socio-political and material-economic conditions in which practice is enacted (Kemmis et al., 2014). As such, preliminary approaches for implementing the English Language Policy at our university have involved an initial diagnostic process at the course level to determine the aspects of the practice architectures that enable and constrain implementation. To illustrate the process and findings from this kind of diagnostic analysis, this paper reports on one study of a professional Masters by coursework degree that targets students from diverse cultural, linguistic and disciplinary backgrounds. The presentation will begin by describing the principles of the English Language Policy and the context of the Masters course. It will then outline the methods, which include interviews with course and subject coordinators and the analysis of course and subject material. It concludes by presenting the initial findings of existing practice as compared with the principles of good practice to accompany the English Language Policy. We argue that this data can inform teaching and learning leaders to take an evidence-based approach to changing the practice architectures for long-term sustainable change. We also suggest that practice theory offers a productive way forward for operationalising policy in a complex environment.