I'll add a couple more. AUP Begin with a simple, straight forward, easy to read and understand, single page acceptable use policy. This won't guarantee that parents will actually read it before signing but will make it much harder for them to claim that they thought they were signing some sort of field trip release form or sports permission slip. This may surprise some folks but there are kids who can sit through a whole class and not remember one thing. That's why there needs to be some form of assessment after the Internet training.
Students have to prove that they heard and understood what was taught.
This way, students can't say they didn't know the Playboy Website was inappropriate and off limits. Along with monitoring there has to be an unambiguous and clear cut set of consequences laid out for students who willfully violate Internet use guidelines. In case all the above might fail there should be in place some form or blocking or filtering software to act as a back-up or adjunct to the watchful eye of the teachers. If given a choice between a 14 year old with too much time and opportunity on his hands and filters, AUP and Internet training, my money's on the 14 year old. Their case would be very weak because the above 6 points demonstrate that everything possible was done to ensure that students used the Internet properly.