This study investigates the effect of corpus consultation on the accuracy of learner written error revisions. It examines the conditions which cause a learner to consult the corpus in correcting errors and whether these revisions are more effective than those made using other corrections methods. Claims have been made for the potential usefulness of corpora in encouraging a better understanding of language through inductive learning (Johns, 1991; Benson, 2001; Watson Todd, 2003). The opportunity for learners to interact with the authentic language used to compile corpora has also been cited as a possible benefit (Thurstun and Candlin, 1998). However, theoretical advantages of using corpus data have not always translated into actual benefits in real learning contexts. Learners frequently encounter difficulties in dealing with the volume of information available to them in concordances and can reject corpus use because it adds to their learning load (Yoon and Hirvela, 2004; Frankenberg Garcia, 2005; Lee and Swales, 2006). This has meant that practical employment of corpus data has sometimes been difficult to implement. In this experiment, learners on a six week pre-sessional English for Academic Purposes (EAP) course were shown how to use the BYU (Brigham Young University) website to access the BNC (British National Corpus) to address written errors. Through a draft/feedback/revision process using meta-linguistic error coding, the frequency, context and effectiveness of the corpus being used as a reference tool was measured. Use of the corpus was found to be limited to a small range of error types which largely involved queries of a pragmatic nature. In these contexts, the corpus was found to be a potentially more effective correction tool than dictionary reference or recourse to previous knowledge and it may have a beneficial effect in encouraging top-down processing skills. However, its frequency of use over the course was low and accounted for only a small proportion of accurate error revisions as a whole. Learner response to the corpus corroborated the negative perception already noted in previous studies. These findings prompt recommendations for further investigation into effective mediation of corpus data within the classroom and continued technological developments in order to make corpus data more accessible to non-specialists.