This happened during my schooling, whilst at High School and in 6th Form College (Ages 15-18) and there was a rather lengthy debate about it and then after that failed to solve the issue the rest of the years were spent combating the system admin for the school, who was a dubious character before this altercation started.
Now in my eyes, and I admit I am not fully versed in technology or privacy laws but will argue from precedent, that they are obviously allowed to monitor traffic on their network, however this is not the same as monitoring what you do on your laptop, there is this line of ownership there.
If it is merely a screen watching program or service, then it is allowable but still immoral as there should be a teacher there in the room who can perform that function and no back-tracing to the computer in question should be allowed as that is often interpreted as hacking especially if done covertly. Most schools have this installed on their own computers but there should be no obligation to install it on yours.
On the other hand, if the system is actually looking through your files, processes and applications whilst on the system, so it is controlling instead of viewing then it is illegal as that is your property and they need your permission just like you need theirs to save and access on their network.
Although I will say there is no need to access porn from school, but flash games at lunch are hardly going to forfeit your entire year of learning, there needs to be a bit more moderation in terms of enforcing rules and regulations like all things in past years when people were allowed to make an honest mistake and not get crucified for it then they often learned from it and were thankful, but now if people are punished for minor infringements they often end up doing it again to "get back" at the enforcers.
Sorry if I'm not adding much to people's thoughts but just trying to condense the argument against.
