The purpose of this study is to determine whether differences in academic attainment between university students could be correlated with their use of English for academic purposes. Using the diagnostic language assessment procedure known as Measuring the Academic Skills of University Students (MASUS), as well as informal analysis of assignment feedback and interviews with students, students' performance in assignments in three subject areas was investigated. Results confirmed that there was a strong correlation between the overall scores students obtained in the MASUS language assessment and their attainment as represented by their assignment grade. However, analysis of the five separate categories of the MASUS scores showed that only the scores for the category, "use of source material," correlated strongly with student attainment and that the scores on the more explicit language categories, "structure and development of the text," "academic writing style," and "grammar," did not. The paper considers the implications of these findings for future studies of the role of English for academic purposes in students' attainment and for EAP pedagogy. (Contains 1 table.)