I don't know if you are an Apple FAN or not but in AT&T terms, having a student discount indicates that you receive what is know as a National Account Discount (NAD) and this is indcated by a Foundation Account Number (FAN) that is assigned to your AT&T account. This magic FAN determines what discount you receive from AT&T.
When you log into AT&T's portal
http://www.att.com/olam on the main portal page (upper right banner section) you will see a Number ( this is your FAN ).
The quickest way to know if you can purchase at Apple is to go to the Apple site and check your Eligiblity. Here is the direct link:
https://buyiphone.apple.com/WebObjects/IPACustomer.woa/wa/IPAToolAction/checkUpgradeEligibility
You will get an error message if Apple is unable to access your account. No error means that your FAN is not a problem. Having a FAN tied to your account is not the major issue with Apple accessing your account, the biggest issues the type of account. For some silly reason, AT&T chose not to share all of it's business accounts with Apple, go figure...
Dave