Facilitating students' critical thinking in asynchronous discussions is important in online learning environments. Since students need to be self-regulated in online learning, the instructors are expected to scaffold students by providing structure and guidance. This paper discusses critical inquiry in two groups of students' online discussions. One group of the students received training in using the practical inquiry model to regulate their online discourse and code their posts. The other group of the students were informed of the model, but were not trained to use the model as a self-regulatory tool and code online posts. It was found that the former group of the students demonstrated higher level critical thinking more frequently than the latter group of the students. The results indicated that using the model as a self-regulatory tool by the students could facilitate their critical inquiry in online asynchronous discussions. Training students to use the model for self-regulation is also discussed in this paper. (Contains 4 tables.)