While it is accepted that English language proficiency is predictive of academic success at university the nature of difficulties faced by students with limited language skills and the means by which they can be readily detected and addressed are not well understood. As numbers of international students who are not studying in their native language rises this omission is becoming of increasing importance. As in many other faculties, the University of Auckland Business School provides supplementary tutorials and support to students in an effort to build language skills. In common with the majority of such programmes designed for higher education students our programme focuses on developing academic writing skills and students are often persuaded to accept intensive support only after they have experienced some sort of failure or difficulty. In this paper, we briefly describe 'DELNA', a screening and diagnostic tool, used at the University of Auckland and, using a sample of approximately 4000 students undertaking business courses, we demonstrate the predictive power of the tool. In further analyses we identify the relative contribution of reading, listening and writing to course performance. Our results unexpectedly revealed that reading had far greater predictive power than writing. We interpret our results as a reflection of the challenges students face in accessing curricula rather than in expressing and documenting their ideas. This work has important implications for the support we offer students and for our teaching and assessment practices, particularly during the first year of study. In our presentation we will share both our theoretical interpretations and the programmatic changes we have introduced as a consequence of the study.