Let me correct your question; UNsubsidized federal loans accumulate interest while in school, grace, deferment, etc....
To answer your question; Perkins loans are Subsidized, they accumulate no interest while in school, grace, deferment. But buyer beware, Perkins loans are evil, stay away from them. Since the current interest rate is below 5%, when you consolidate your loans, the Perkins loans will screw you and drive up your final consolidated rate. Now, if the interest rate was above 5% (which it is not currently and will not be next year), it will do the opposite.