Recent research into the merits of online discussion (computer-mediated communication) has shown that it promotes active learning behaviors and enhances learner outcomes. Scholars have also shown that, when instructors employ effective questioning and moderating skills, students can show higher levels of critical thinking in online discussion. In an investigation that merged and refined content analysis protocols in order to identify the effects of such factors as student GPA and type of course upon student engagement and student critical thinking, our findings substantiate a link between student interaction and critical thinking. When students engage one another in online discussions in a focused way, their capacity for reasoned discourse becomes more evident. (Contains 16 tables.)