A comparative case study used content analysis to observe the emergence of voluntary online learning communities in two blended courses. The study developed an interaction-based approach to analyze such communities, and found interesting similarities and differences between the two classes. One similarity is the emergence of three categories of students in each class: Core, Active, and Peripheral. The distribution of students into these three categories was almost identical, and appears to be similar to the widely observed bibliographic distribution regularity known as Bradford?s Law.