Of those blog systems the only one I have experience with is WordPress and it certainly has the features you want. Pupils would have to register on a single blog however for the teacher to be able to moderate them effectively. The teacher could go setup 30-40 blogs and then give pupils the limited access required but who has time for that? There is no “global moderation” of comments and posts in a multi-blog environment.
Just install WordPress and use one blog for the whole class.