Teens in school might think twice about taking any sort of drug if they knew they could be randomly tested and reported to their parents as well as to authorities and have consequences at school. It might not solve the drug problem but it could hardly hurt and might do some good for some kids.
If you have random drug testing I schools it will cause for the kids to think a bit more before using any kind of drugs because they will be thinking that it is more possible for them to get caught. I think it would also deter people from selling to kids because they will not want the drugs traced back to them.
As any parent knows, there is nothing that will deter their children from trying drugs if they want to. Drug use and abuse in children is not something that schools should be involved. If schools find a students drug use to be disruptive, then they should involve both the child's parents and the authorities. That is as far as schools should have the right to go.