This type of IRS letter is usually a result of your school not issuing a form 1098-T or issuing a 1098-T with box 1 blank. The IRS computers match their copy of the 1098-T (or lack thereof) with you tax return.
Yo now need to prove you paid qualifying educational expenses (tuition fees and course materials). Put together a list of what you paid for and sign it. Attach copies of school billing statements, cancelled checks and/or bank and credit card statements to prove you paid.
