You have to fill in a form from the College / School, which should be signed by the principal and then take it to the PRS ( In case of Reservation) or URS ( Unreserved ticket) and then submit there. He will tear a portion of it and then give you the ticket as well as the rest of the portion.
The students concession will be valid ONLY IF you submit it to the TTE along with the portion the counter person gave you.. Else you will be asked to pay the rest amount.