These sites provide a window within a window. The school, home or government computer registers that the user has gone to the proxy site..... and stayed there. The inner window then allows the user to go anywhere, look at anything without any trace.....
As in so many areas of law enforcement (in or outside school), the only real deterrent is a "climate of fear" regarding severe and public punishment for offenders caught by traditional methods - surveillance, informers, mistakes by the perp (e.g. storing images on local machines for later viewing).
Stephen Digby