I am wary of using multiple parent modules for larger sites in case a site wants to branch out on it's own. My fear is that it would be hard to separate. Plus I think each educational institution will want their own instance of DNN. There are some aspects, however, that we would like to share. I know there are modules to share between portals, but what about modules to share modules between dnn instances(eg separate installs). For example, we would to share our text based repository module and our wiki modules so that each institution can contribute/edit and share content. Social interaction and interaction between websites (and even portals) would be a huge plus for dotnetnuke. It may require adding columns to all modules with a unique instance identifier (rather than just portal id). Perhaps it could be customized to something like 'whs' for west high school, for example

Thanks Sebastian --
I'd want to do more than share content -- also share functionality.
e.g. allow each site to modify the same wiki module.
Perhaps this could be done on a completely separate database that the module connection string connects to.  Then would need to add a column with an institution identifier?
Perhaps modifying core repository module, for example, and just connecting it to a separate external database.