In general, students should expect less of a right to privacy while they are in a school environment than anywhere else. In public, students are citizens like anyone else. In school, they are in a specific situation with specific governmental goals that override some of their privacy rights. In the US, this can be seen in cases such as New Jersey v. T. L. O.
The basic idea is that the main purpose of a school is to educate and that the school has a compelling interest in doing that as well as it can. Therefore, the school is allowed to violate student privacy when such a violation is necessary in order to maintain a good, safe, learning environment. Because of this, students are subject to more invasions of their privacy at school than when they are in other environments.
Ellen, TLO forbids "at will" searches.
other than your physical person you have no expectation of privacy in a school or on its property. tThe lockers and desks belong to the school giving them the right to access at will, your backpack and person can be search for safety...similar to the Terry stop laws. demeaning searches such as strip searches have been found to be a violation of students civil rights particularly when dealing with minors