This study assessed the impact of completing an English for Academic Purposes (EAP) course on the writing of postgraduate learners. We begin this paper by describing a course offered for credit to postgraduate international students at a university in Australia, and then report on a large-scale study (n = 69) which investigated the improvement (if any) in the writing of students enrolled in this course. The students undertook the course at the beginning of their postgraduate studies at the university and concurrently with their degree programs. Two cohorts were identified: students with an IELTS score on entry to the University of 6.0 (or equivalent) and those with a score of 6.5. Data for the study were the in-class writing produced by the students at the beginning and at the end of semester, and a short questionnaire. The students' texts were analysed using a range of measures for fluency, linguistic accuracy and use of academic vocabulary. Texts were also analysed for overall structure, cohesion and coherence. The study found improvements for the entire group and for the two cohorts mainly in terms of accuracy, use of academic vocabulary, and structure. We discuss these findings in relation to key pedagogical features of the course. (Contains 9 tables.)