This study aims to investigate the usefulness of a deductive-cum-process writing approach to raise native Cantonese-speaking ESL students' awareness of the inappropriate use of informal language in academic writing. Achieving tone formality by incorporating appropriate syntactic and semantic elements poses great difficulties to freshmen at the City University of Hong Kong. Furthermore, the effectiveness of using a deductive approach to teach word usage has been inconclusive despite numerous studies on this issue (e.g., Alzubi, 2015; Tammenga-Helmantel, 2014; Vogel, et al. 2011) . In the current study, seven types of informal language expressions and corresponding formal alternatives were first taught, followed by peer review and individual teacher-student consultations to reinforce the teaching. The experimental group consisted of 19 students taking an academic writing course in the summer semester 2017-18. The end-of-course written examination showed that the experimental group used significantly fewer informal expressions than did the control group in three measures -- the total number of informal expressions and two component measures (p[less than or equal to]0.05). Questionnaire findings confirmed the usefulness of the current teaching approach, as perceived by the majority of the participants. Qualitative analysis revealed informal expressions that were most difficult for the participants to identify and to make correction. [This paper was published in "English Language Teaching and Linguistics Studies" v2 n2 p21-42 2020.]