One way is through education. Schools can conduct regular seminars or classes on appropriate behavior and ethics. Teachers can also be vigilant in the classroom and report any signs of such inappropriate stories being spread. Additionally, schools can use technology to monitor and block any inappropriate content on school - provided devices.
Schools can prevent the spread of such inappropriate stories by having strict code of conduct policies. They should clearly state that any form of sharing or creating nude - related stories is unacceptable. And those who violate the policy will be punished severely.