Is it a bonus under TISA/Regulation DD? No, and you have cited the reason why.
Is it interest for IRS purposes? No, because interest is a payment for a deposit of money, and you are paying for grades.
It would be a reportable payment under 1099-MISC rules if the $600 trigger is met.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8