I don't know if its been to the supreme court yet? I know that at work we were given security locks to keep classified data in. Only the security officer had the combination. We used these "safes" for very valuable things in addition to classified papers, one employee had a diamond necklace in his safe when it was inspected for a security audit. After this we were all told the safe was the company's property and we could be fired for keeping personal stuff there. Likewise they could search briefcases and cars. We knew all this when we went to work there and undoubtably signed some consent somewhere along the way. I think this is how to handle school kids, let them sign contracts, get their parents to sign too, since kids are not of legal age, and have them understand what "rights" they have and what they must live by to attend the school. Some schools have these contracts, they also delineate the punishment for bringing a weapon to school for example, it still does not sink in to kids cause they are (many of them) too immature to understand what they agree to and what the consequences will be.
I know its a government school, but this is something that is handled with local control. Schools in high crime areas DO have a drug problem, and while kids could handle their dealings on the street, most of the dealing is done right under the noses of the school administration. Additionally when a kid reports a valuable thingy has been stolen, there may be a cause for a search warent. I don't know how much good having the kid's family go to a judge would be, but kids who steal things (that other kids should not bring to school anyway) should get caught and be expelled. The punishment should fit the crime. Involving the higher levels of society, like police, DA's and judges would be a learning experience but many in school are not ready to be taught this lesson. When the school handles it, often times there is no permanent record, so the kids may come out of it better off than if the criminal justice system was used.