They have a right to able to search your backpack.
They do have a say in that you cannot search there backpack without permission.
The supreme court states that you don't need a warrant in order to search a students backpack in a public school.
The search did not violate the constitution, so they put more reasonable rules in schools.
It didn't because it didn't violate the constitution they just made more reasonable requirements.
Credits:
Created with images by Activedia - "law justice court" • albertoziveri - "Incase Backpacks" • Johnragai-Moment Catcher - "Where is my passport?" • dbking - "US Supreme Court" • brettneilson - "Declaration of Independence" • gnuckx - "Palestine_Gaza_NK20210"