And, using the field trip example again, there *are* legal implications to taking students on a trip. That's why we have permission slips.
Legal reasons are surmountable if you are doing something reasonable.
Don't abandon your idea before you even try it because thinking about the "legal implications" is complex.
In the case of having a student intranet I think there are basically ZERO legal implications since everything the network would do already exists in a school.

