Planning and coordination of projects and project components lend themselves to a collaborative web solution. Do it, do it, done is a free web service to create and manage to do lists. No registration is required - all that you need to do is remember the key to get back to your list!
Of course, a collaborative calendar would be a nice addition to display tests, assignments, and other due dates. If you are using any of the other collaborative environments, they probably have an integrated calendar and that would be a better place to host a calendar. But, if you want just a calendar...