I was able to add a student discount to my line today by calling 1-877-453-8824. This is the migration department. The number was given to me by an online chat rep. The discount varies by school. If for some reason your school is not on the list, you can also register your .edu email address with StudentRate.com and get a 10% discount.
One note - if you have a discount plan already (for example the no-longer-available Unlimited Loyalty Plan) you may have to change your rate plan to one that is currently being offered in order to receive the discount. However, it my understanding that if you do the discount through StudentRate.com, it will apply to any plan (current or formerly offered) as well as data/text/etc.
Hope this helps... when in doubt I would just call and ask!