Background: Instructors often try to promote student engagement with discussion boards in learning management systems (LMS) like Canvas. Although convenient, alternatives like the social media platform Reddit may be more effective. Method: A non-randomized controlled trial compared the use of Canvas and Reddit in two sections of two undergraduate psychology courses (N = 77). Engagement was measured as the number and word-count of posts and responses and complemented with self-reported data. Results: There was no difference between platforms in total number of posts or replies. In one course, the average word count per post was higher in Reddit than Canvas (r = 0.44). However, in the other course, the average word count per post (r = 0.47) and per reply (r = 0.39) was significantly lower in Reddit. Neither course observed a significant difference in students' perceived value of the discussion board. Conclusion: This study provided no consistent evidence that Reddit supports student engagement relative to Canvas, and combined with additional survey data, it is possible that hosting the discussion board on Reddit may even be detrimental.