Does a police officer need a warrant to arrest someone at school?

Officials in a school (and many other institutions) have a duty of care to ensure the safety and well being of people within the school. In some cases, the ability to search a student may be vital to ensure the safety of others. There are other situations where the ability to search students would be equally important. It is a power that should never be abused but to deny the power to school staff is to prevent them performing their duties in the best way possible.