The focus of this study was on teacher cognitions and the teaching process within online classrooms. In particular, this study was intended to explore teachers' teaching methodologies when performing grammatical instruction for relative clauses, whether they applied an inductive or deductive approach. The rationales of this study were to examine teachers' cognitions and maxims (decision-making processes) for their teaching methodologies when they teach relative clauses, one of the grammar lessons within the online classroom. The purpose of this study was established to elucidate these mental processes and to understand the methodological strategies teachers employ when teaching relative clauses.Findings from this research indicate that the teacher participants engaged in similar processes when teaching relative clauses. Even though they requested their students to notify or identify the functions of 'who' and 'which' in the relative clauses from example sentences, they still tended to use deductive approaches to teach their students. Half of the students reflected that their teachers taught using deductive methods. The research results were not consistent with my assumption at the beginning of this study. The results indicated that teachers' teaching methodologies are constructed by their educational programmes, pre-teaching training courses, teaching experiences and socio-educational contexts in the ESL teaching environment; they are not mostly influenced by cultural backgrounds, as I had presumed would be the case. In the following paragraphs, a summary of the research results, their implications for pedagogical methodology, research limitations and speculations will be stated and discussed.