This paper explores the practicum experience of a group of bilingual student-teachers who taught Chinese using English to learners of Chinese as a foreign language (CFL) in Western Sydney schools. Specifically it explores how these student-teachers used English as the instructional language in class and what strengths and weaknesses they demonstrated compared to their host teachers. Data were collected through observing and audio-recording the participants' teaching, aiming to capture the actual features of their English use in class. The data were structurally-coded employing the ELM categories. Discourse analysis was employed to interpret and understand the language use of the bilingual student teachers and also their supervising teachers. The bilingual student-teachers in this research, whose English proficiency was at IELTS 7.5, and who had experienced six months of intensive teaching practicum, were found able to demonstrate grammatically and discursively acceptable expressions throughout their teaching. The difficulties experienced by this cohort were more due to their lack of skills and flexibilities in teaching and classroom management rather than their inappropriate use of instructional English. (Contains 3 tables.)