Sync still takes too long
Even with just 2 users, the sync experience is variable and nowhere near as consistent with Google Docs. Sometimes the notebook has to be manually synced, other times it works automatically. With more active users in a class notebook the problem is worse.
To reduce the overhead of a class notebook constantly syncing there could be an option to set how often the teacher would like all users and clients to sync. For example, if the teacher is just sending out a page with instructions for pupils to refer to then the sync frequency can be reduced to a default (e.g. 1 min) but if the teacher is wanting real-time collaboration then they can set it to constantly sync.