This study draws on the strengths of both corpus linguistics and critical discourse analysis approaches to investigate the issues of power and ideology of teachers evident in their language use in the discussions on Ajarn.com. Data collection involved constructing a corpus from the discussions on the website, with the discussion threads dated from 2012 to 2022, in the "Thai students" tag. Altogether, the corpus, named Discussion corpus, covered over 80 articles with more than 160,000 words. Utilising Wmatrix software to generate semantic tags of the words in the corpus, an analysis of thematic categorisations revealed that issues related to education were central to the teachers' discussions. In addition, an analysis of verb collocates of "students" using AntConc software confirmed that teachers expressed their dominance over the students in different ways. Interestingly, it was also found that teachers felt that they could become powerless in a specific context in a bureaucratic system. Overall, this study, acknowledging that power is a fundamental part of social relations, suggests that teachers should exercise their power in a healthy way that benefits students' learning.