School authorities are currently allowed to check students' lockers and backpacks if they feel the student is breaking the law or posing a threat to the safety of the school. They do not need a warrant or standard of proof, like the police must have when searching someone's property. Some feel this is an invasion of privacy, and several arguments have been posed against this practice.
Invasion of Privacy
School authorities should follow basic procedure that the police do, requiring "probable cause" to search someone's belongings. The Fourth Amendment of the U.S. Constitution guarantees protection from unreasonable search and seizure. The Universal Declaration of Human Rights also guarantees against "arbitrary interference" with privacy.
Treating students as sub-adults can be a factor in increasing alienation and detachment from a school surrounding. If students don't feel they have a safe space at school, they have a lessened tendency to work hard, go to class, or even enter the building. Providing students with their own space, like a locker, serves as an anchor in the school setting.
Students trust teachers to carry out searches with objectivity as disinterested parties. However, there's no guarantee that a teacher might not use a search on a student's belongings as a way to carry out a grudge, since the standard for search is so low. Also, if search occurs in public, as they often do, and turns up embarrassing things such as contraceptives or medications, it can result in humiliation for the student.
Infraction of Basic Rights
Students are human beings protected under the law, as are adults--in fact; they are given extra rights in certain cases, such as when entering a contract agreement. Considering them suspect as the default, and not giving them the benefit of the doubt, is a failure to sustain basic rights of a person under the law.
Backpacks vs. Lockers
Although lockers may be considered school property on loan, and therefore subject to a lessened standard of search, backpacks are purchased and owned by the student and should be considered personal property. Backpacks' mere presence on school property does not convert them to school property.