Although they are outside credit unions' traditional line of products, private student loans present an opportunity to help families pay for college when scholarships, grants and federal loans are not enough to cover the rising cost of attendance.

"I think it's crucial that a credit union be considered a full service financial institution and offering student loans is one part of that essential mix," said Dennis Dollar, principal partner of credit union consulting firm Dollar Associates. "So whether it be through direct lending or through a referral program, I believe that credit unions must offer student loans."

Hundreds of credit unions have signed on with Sallie Mae's Smart Option Student Loan referral program. The loans are underwritten, funded and serviced by Sallie Mae; participating CUs serve as a referral point via a link on their website.