SUMMARY
An aspect of vocabulary research that tends to be somewhat neglected is that based on qualitative investigation. While a number of studies have considered the differences in vocabulary size between first-language (L1) and additional language (AL) speakers of English, there has been relatively little in-depth investigation into the nature of the vocabulary differences between these groups. The aim of this paper is to shed light on some of the vocabulary features of both L1 and AL student writing in relation to published writing as a benchmark. This study is based on the results of a qualitative investigation conducted using a corpus-driven approach which focused on differences in the use of academic vocabulary by both L1 and AL groups across first-, second- and third-year psychology students. The method used to identify vocabulary differences was keyness analysis, in which vocabulary items are compared on the basis of significantly different frequencies. One of the patterns that emerged serves to support the assumption that L1 students have a better grasp of academic vocabulary than AL students, as there are a greater number of grammatical, semantic and collocational idiosyncrasies in AL writing. The analysis also confirms that high achievers tend to use a broader range of academic words than low achievers. Given the evidence that a good knowledge of academic vocabulary in particular is essential for success at the level of tertiary education, the results of this study contribute to the question of what the specific vocabulary needs of undergraduate students are within the university context.