"[D]oes this mean that the prospects for student loan delinquencies are similar to those for the household debt in general, and thus no special attention is warranted? Unfortunately, this is not the case—some special accounting used for student loans, not applicable to other types of consumer debt, makes it likely that the delinquency rates for student loans are understated.
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From this exercise, we find that as many as 47 percent of student loan borrowers appear to be in deferral or forbearance periods, and thus did not have to make payments as of third-quarter 2011. Specifically, 17.6 percent of borrowers had exactly the same balance in the third quarter as in the second quarter of this year, and 29.1 percent increased their overall student loan balance by taking on new originations or accruing interest to the balance.
We then recalculate the proportion of borrowers with a past due balance excluding this group of borrowers. We find that 27 percent of the borrowers have past due balances, while the adjusted proportion of outstanding student loan balances that is delinquent is 21 percent—much higher than the unadjusted rates of 14.4 percent and 10 percent, respectively
http://libertystreeteconomics.newyorkfed.org/2012/03/grading-student-loans.html