The First Presidency has said: "'...one-tenth of all their interest annually,' which is understood to mean income. No one is justified in making any other statement than this."
So, is a loan income? By no logical measure I can think of since you have to pay it back with interest. Pell Grant is more tricky since you don't have to pay it back, coupled with the "you are getting this grant for education only and are forbidden to use it for other purposes" sort of idea. But, I am not justified in making any statement beyond, "your income annually". Pray and go. You answer the "are you a full tithe payer" question to the Lord via the bishop. We would all do well to not justify, but the Lord is pretty smart, and we should try to be as well. He is also perfectly honest, and we need to do our best to be the same with Him.
Good thing He loves us all - imperfect as we are, eh?
