When viewing old schools on aerial maps, look at the adjacent fields in the area also. Faint trails or patterns can indicate high traffic areas, or even better, old ball fields.
Look for rectangle shapes that may indicate the side lines of an older football field. Triangle or pie shaped lines may indicate an old baseball field.
Aerial maps can be a great way to scout for areas to detect that are hard to see from the road. With a little effort you may be able to find yourself a honey hole on some previously undetected ball fields or old drive-ins.
Check out Historic Aerials for satellite and topo maps going back into the 1930s.