First, you must contact the College or University Accounting Department in order to inquire on why they have reflected the amounts differently this year.
Second, the difference in the amount should not affect your eligibility for the American Opportunity Credit unless the entire amount in Box 2 is covered by a Grant and/or Scholarship. If you paid this tuition amount, $4500.00 out of pocket, you have actually exceeded the maximum amount allowable for the Credit by $500.00.
The only other section in Form 1098-T that may be keeping you from the AOTC is Box 8. This must be checked to indicate that you are at least a Half-Time student.
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