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Cosigning does not make the borrowed money a payment from you so we have to look at the rules when the dependent pays the expense.
The rules for the tuition deduction are tougher than ther rules for the tax credits:
If your dependent pays qualified education expenses and you can claim an exemption for your dependent on your tax return, no one can take a tuition and fees deduction for those expenses. Neither you nor your dependent can deduct the expenses. For purposes of the tuition and fees deduction, you are not treated as paying any expenses actually paid by a dependent for whom you or anyone other than the dependent can claim an exemption. This rule applies even if you do not claim an exemption for your dependent on your tax return.
For the Hope and Lifetime Learning Credit:
If you claim an exemption on your tax return for an eligible student who is your dependent, treat any expenses paid (or deemed paid) by your dependent as if you had paid them.
Someone other than you, your spouse, or your dependent (such as a relative or former spouse) may make a payment directly to an eligible educational institution to pay for an eligible student's qualified education expenses. In this case, the student is treated as receiving the payment from the other person and, in turn, paying the institution. If you claim an exemption on your tax return for the student, you are considered to have paid the expenses.
See Publication 970 for more details.
It appears you should try the credits to see if there is more benefit than the deduction. The only way to know for sure is to compute the return each way and compare.
I hope this helps.