This article is from the Financial Aid, Scholarships, and Fellowships FAQ, by Mark Kantrowitz with numerous contributions by others.
Not immediately. The subsidized Stafford loan has a grace period
of 6 months and the Perkins loan a grace period of 9 months before
the student must begin repaying the loan. When you take a leave of
absense you will not have to repay your loan until the grace
period is used up. If you use up the grace period, however, when
you graduate you will have to begin repaying your loan
immediately. It is possible to request an extension to the grace
period, but this must be done *before* the grace period is used
If your grace period has run out in the middle of your leave, you
will have to make a payment on your student loans.