Hi,
I work for Nedap Education who supply an e-registration system that integrates with most major MIS Systems.
Our systems use RFID cards issued to students and we can supply a mobile data logger unit about the size of a large keyring, that reads upto 1000 cards and then stores the data in the unit until it's plugged into the USB Cradle on a PC and downloaded into the system.
It's offline data capture, but small, robust and doesn't require any sort of data plan or other device.
Regards,
Ross