This study seeks to understand instructors' perceptions of social network analysis (SNA) and network visualizations as learning analytics (LA) tools for generating useful insights about student online interactions in their class. Qualitative and quantitative data were collected from three graduate courses taught at a Canadian university at the end of the academic term and came from two sources: (1) class-wide forum discussion messages, and (2) interviews with instructors regarding their perceptions of student networks and interactions. This study is unique as it focuses on instructors' self-assessments of online student interactions and compares this with the SNA visualization. The difference between instructors' perceptions of social network interactions and actual interactions underlines the potential that LA can provide for instructors. The results confirmed that SNA and network visualizations have the potential of making the "invisible" visible to instructors, thus enhancing their ability to engage students more effectively.