If the school was built in the 40's that is 60 years of loosing coins in a confined area. A lways ask permission when hunting the places mentioned above. It is not hard to get permission to hunt at a church. Remember, it is open every Sunday. Go early and ask to hunt at another time when they are not so busy.
Schools are the same way.
Just go in to the main office and ask. Make sure you point out that you WILL be returning lost class rings and other identifiable items. For public parks it is best to inquire at city hall. Better yet, ask the local police. They are the ones that enforce the laws concerning coin shooting.