Note that while all iPhones have GPS location, only iPads with cellular antennas have GPS location built in (but you don’t need to have a cellular contract for the iPad in order for the GPS to work). Because cellular iPads are more expensive, most schools opt for WiFi-only iPads. These would not have the GPS radio/antenna and might not give accurate locations. Granted, most areas with lots of WiFi access points can be geo-located due to projects like Skyhook that have mapped WiFi hotspots. You don’t need to actually be connected to any hotspot for it to work, just the presence of multiple hotspots allows most devices to track your location.
To be sure, take a WiFi-only device to the actual location(s) you want students to use. If you are able to get location in a standard maps app, you should be fine.