What are the laws regarding internet privacy and schools?

[Jon]

Since the material is in public view, the school staff can read it just like anyone else can.

The school is certainly within its rights to punish pupils for posting rude comments about teachers or other pupils, but if it stopped pupils making fair and accurate comment which was unflattering to the school (e.g. if someone truthfully posted that bullying was common as the staff failed to keep order, or that the roof leaked) that would be much more open to challenge.