Elgg

Found this blogging tool aimed at educational institutions. It might be worth a try:

elgg.net :: the learning landscape: "The concept behind the system is to develop a fully customizable learning landscape. To achieve this Elgg is a hybrid of weblogging, e-portfolios and social networking. It is hoped this combination of features will provide an engaging environment for learners to create their own learning space and then connect to others, forming online communities of learning."