Mainstream schools in particular have a duty of care towards minors. To this end, advice, clear teaching and Acceptable Use Contracts are not always sufficient. In a previous life-form it was my responsibility to ensure an e-safe working environment which included all of the above. However, it was, for the children, the fear of being found out, with date-stamped hard-copy, that really won through.
This is now a feature of our eFolio system that any suspect child or reported incident can easily be checked out. Again, regular alphabetic or random trawls can also ensure that reasonable on-line behaviour is occurring.
I do not think that where an e-safe system with published rules and sanctions is in place there should be any problem. After all, the institution's system is there for work and, like any exercise book, the ePortfolio, although deemed to be owned by the student, is still open to view by any teacher, parents and mentors or even the Headteacher or a Schools' Inspector!
Increasingly, students of any age can use their own systems for collaboration or investigation and can reserve any 'non-school' activities for systems external to the institution. So much so that some children have objected to their school's use of FaceBook as an intrusion upon their private lives.