Forum .LRN Q&A: Response to An educational blog app
The use case you raise is an interesting one. I'm imagining that the teacher would want to give each group its own subgroup to work in so they can share file-storage, discussion boards, group-internal deadlines on the calendar, etc. Given that situation, you'd want the group to be able to work out their blogs together and then publish the results to the class level.
Now, how would the publishing process work within the group? You have two pieces to the workflow that require very different social actions. First, the group has to decide which posts are worthy of publishing. This requires consensus-building. Then somebody has to pull the switch and actually publish. This is more of an executive act. You could use a general-ratings package as a voting mechanism within the group. Once a consensus (or, at least, a majority) is established, somebody could be assigned the privilege of flipping the switch to publish the group's choice(s) up one level to an aggregation portlet for the class blogs.