This study focused on the effects of peer moderation on meaningful interactions in online discussions. A meaningful interaction was defined as a message relating to a discussion topic, responding to a previous message, and adding substance to the discussion. A randomized-subject, posttest-only control group design was used to test the first hypothesis, that a peer-moderated online discussion forum would contain more posts responding to previous comments than a nonmoderated forum, and the second hypothesis, that a peer-moderated online discussion forum would contain more substantive responses enriching the conversation than a nonmoderated forum. Both hypotheses were supported. Results showed that students responded to messages more actively and engaged in more in-depth discussions when discussions were moderated by a peer.