Security on school networks

On my school's network, everyone in the same class shares the same account. Everyone also puts their files on the same account. This means that anyone in the class can delete or change anyone else's files very easily. To add to this, half of the class accounts in the school have no password at all. Because of all these security problems, I put all my files on my USB drive and not on the school server. Every year half of all students have their files altered or deleted about five times a year. I used to have my files deleted every second day. I thought about making everyone have a seperate account, but each computer is used by two people at a time making everyone having their own account anyway impossible. I need a way to secure people's files on the server easily.