||Many ESL/EFL learners find it difficult to write argumentatively, because unlike L1 students, who usually only have to attend to the quality and organisation of the arguments, L2 students also have to ensure that their language is grammatically correct and accurate. Since it is difficult for L2 learners to improve their accuracy quickly, the question explored here is whether the use of an effective argumentative structure and/or a favourable language environment can be conducive to successful L2 writing. The objectives were threefold: firstly, to explore how effectively L2 tertiary students build up their universe of argumentative discourse, from the lowest discourse level to the highest; secondly, to examine whether compared with an EFL setting, an ESL environment can bring improvement in organisation and grammatical accuracy to students’ writing; and finally, to test the correlation between the holistic grades awarded to essays and their quality as determined by analytical measures of argumentative coherence and grammatical accuracy. All the subjects of this study were Hong Kong Chinese, first-year EAP students at Macquarie University, Australia, and the Hong Kong University of Science and Technology, thus studying in an ESL and EFL environment respectively. The data set consisted of twenty-four essays written on an argumentative topic, six high-rated and six low-rated from each group. Two tools were used to investigate the differences between the high-rated and low-rated essays, and also those between Australian and Hong Kong essays: Rhetorical Function Analysis (RFA) was devised to investigate the hierarchical integration of argument, and Grammatical Accuracy Analysis (GAA) was used to study syntactic accuracy. RFA showed that the high-rated essays displayed effective argumentative structures at different textual levels, with appropriate in-depth development of ideas, which all con-tribute to the development of arguments. The low-rated essays, however, were characterised by plagiarism and contextually unidentifiable relations. Their macrostructures did not contribute to the scaffolding of arguments, as these are unclear, contradictory, or even lacking. GAA revealed a surprising similarity in the types of error made by the Australian and Hong Kong subjects, suggesting that not a great deal of development had taken place in the Australian subjects’ English after they had left Hong Kong. Yet there were significant differences in the frequency of some categories of error, showing that the Australian subjects were able to produce more accurate tense forms and idiomatic expressions. There was also less plagiarism in their texts. Though they may not have taken full advantage of the ESL environment, their increased exposure to English seemed to have helped them achieve better approximations toward the target language norms. The findings also showed that independent measures of argumentative coherence and grammatical accuracy correlated significantly with each other, and also with teachers’ holistic assessments of essay quality. This supports the view that pragmatic competence and grammatical competence are interrelated. Effective argumentative structure and grammatical accuracy complement each other; either one of them is a necessary but not sufficient condition for writing success. The fact that increased exposure to everyday English could help the Australian subjects advance a little in grammatical accuracy, but not in organisation, supports the hypothesis that it takes longer to develop L2 learners’ writing competence than oral competence. It also suggests that L2 students need to be taught argumentative structures explicitly. Once they master these, they can concentrate on grammatical accuracy, and become better able to produce essays which are organisationally and linguistically sound, to convey their arguments.