I could be wrong, but I don't think student loans are a revolving charge account, so you wouldn't be "closing" the account in the same manner of speaking as you would be if you closed a credit card account. A credit card account is designed to revolve permanently. A loan usually has a set course it runs in terms of repayments. In other words, the system expects that the loan "account" will ultimately be "closed" (read: paid off) and thus you should not be penalized for paying it off. In fact, from what I understand, it would list as a loan repaid as agreed, which would enhance your credit score.
But as is the case with anything FICO-related, YMMV.