Instructional designers need to be able to assess the level of knowledge construction generated by participants of a virtual learning community (VLC). Such participants include the learners engaged in threaded discussions within online courses. Assessing the level of knowledge construction enables course revisions that scaffold such knowledge construction within courseroom discourse, envisioned as a VLC, in order to increase the quantity or quality of the knowledge construction occurring between participants. Content analysis is an established method used to assess the level of knowledge construction demonstrated in the transcripts of threaded discussions. Yet, researchers have called for the continued use and validation of existing, suitable instruments within content analysis rather than developing researchers developing new instruments that lack extensive use and subsequent validation. In response to these calls, this paper argues that the Interaction Analysis Model (IAM) is an existing, validated protocol for the content analysis of course room transcripts. The purpose of this paper is to endorse the validity of the IAM through a discussion of its development, use, and inter-rater reliability accumulated from 40 published studies spanning 14 years.