Uhm, it's in violation of Sprint policies to do the above also.
Your school usually monitors you as much as any other ISP would. That is, whiel they record the activity, they take no action unless there's a third-party complaint.
Because cell phone connections are encrypted, your school will not be able to see what you do online usign your cell phone. However, given the status quo, I'd be much more concerned about Sprint knowing what you're doing rather than your school.
Or, the easiest solution, if you really have stuff to hide: get a private VPN account. They run $5-$10/mo and have privacy guarantees. You still get to take advantage of the high speed and reliability of your school's connection; or, for that matter, any connection. They're actaully mainly intended for people in oppressive contries, like China.