Bilingual education programmes have become popular worldwide in part because they are believed to facilitate second/foreign/additional language (L2) learning, often with English as the target L2. In such programmes, students learn content and L2 simultaneously, but a common difficulty they encounter is mastering disciplinary literacy in the L2. It has been argued that students' disciplinary literacy will impact their academic performance, particularly in high-stakes assessments of content subjects. However, research exploring bilingual students' development of L2 disciplinary literacy remains scarce.
With a corpus-based multidimensional analysis, this study seeks to explore the relationship between the disciplinary literacy and academic performance of bilingual speakers. A corpus of biology examination essays produced by a stratified sample of students studying in English medium education (EMI) in Hong Kong (204 essays totalling 45,823 words) was compiled. All students sat for the Hong Kong Diploma of Secondary Education (HKDSE) examination, which is the high-stakes university entrance examination taken by 12th Grade (17-18 years old) students in Hong Kong secondary schools. The biology test of HKDSE consists of multiple-choice questions, structured questions which require short answers, and one essay question. This learner corpus only includes students' responses to the essay question because it constitutes the most coherent discourse which reveals students' disciplinary literacy competence. 240 students' scripts from the period 2012-2015, 60 from each year, were randomly selected for our stratified sample. Each cohort consisted of texts that were assigned an overall biology subject grade ranging from U (lowest) to 5** (highest). However, 36 scripts, especially those written by students at the lowest level (U), were excluded from this corpus because they did not reach the threshold word number for the multidimensional analysis (50 words). We used the Multidimensional Analysis Tagger (Nini, 2015) to analyse the linguistic and lexico-grammatical features of the texts and conducted inferential statistical analyses and an in-depth textual analysis comparing the features of essays written by students at different levels of academic performance as measured by their overall subject grade.
The multidimensional analysis shows that this sample generally produced texts which were informational, context-independent, formal and abstract, alike the features of academic prose. In terms of the disciplinary literacy of students with different subject grades, both the quantitative and textual analysis findings show that the essays produced by students with higher grades were more similar to academic prose, consisted of denser and more abstract information and used more academic vocabulary, nominalisation, conjunctions, and passive voice. This study demonstrates a potential relationship between students' mastery of disciplinary literacy and their academic achievement. These findings may imply that, in bilingual education programmes, teachers should not only equip students with content subject knowledge but also develop their disciplinary literacy.
