Only interest is deductible, not the loan balance you pay off.
If this was not a typical student loan lender and you did not get a 1098-E listing the interest, you can still deduct the interest. But, you have to be careful. The loan must have been taken so you could pay qualifying expenses at an educational institution that is accredited to participate in US Federal Student Aid programs, and you must have been attending at least half time as defined by the school. There must also be a direct connection in time and dollars between taking the loan and paying the school. Generally this means you must have taken the loan within "a reasonable time" before or after paying the tuition, and you must be able to show that the loan dollars and the tuition dollars are directly related.
For example, if you took out a credit card loan to pay tuition, and then continued to use the card for unrelated expenses, you would be unable to show that the loan balance was directly related to the cost of education and would lose the deductibility.
Turbotax should allow in the interview, a way to claim student loan interest without a 1098. There may be a checkbox for "I paid interest but did not receive a 1098" or something like that.
