On any available surface. Most notably you can find bacteria at drinking fountains, in the bathrooms, on door handles, stair railings, the cafeteria ... Everywhere. That's why kids get sick and spread germs so easily to one another. Bad hand-washing practices, not covering their sneezes or coughs, putting their fingers in their mouths and noses. The better question would be, "where is bacteria NOT found in schools?" I couldn't answer that one!
