As I pointed out in the challenge, this is a pattern that has been used successfully by a growing number of people in education. As I look at the variations, including examples from my own work, there is a common structure that emerges.
The pattern generally begins with an assignment asking participants to create or contribute some form of artifact. A number of users, from one to many, contribute artifacts at the time the assignment is posted. These initial artifacts are then aggregated by the site creator or curator, and made available to the larger community to review. The site curator often provides some form of initial feedback on these initial artifacts.
The curated list of artifacts is discovered by others on the Web, and this leads to evolving comments and discussions. This dialogue, in turn, prompts others to submit new artifacts which, in turn, leads to more discussion. For some sites this becomes a repeated (and growing) pattern over time.
Sites that use this pattern are intentional about persistence and discovery. Artifacts are curated and shared in a way that makes it easy for others to discover, review, and comment on them. This results in enhanced discoverability and the introduction of new energy into the system.