A group of investors announced plans Monday to buy Sallie Mae, taking the nation’s largest student lender private in a $25 billion deal that comes as some regulators call for tougher standards and lower federal subsidies for the $85 billion college loan industry.

Private equity firm J.C. Flowers & Co. and three other investors will pay $60 per share for the Reston, Va.-based SLM Corp., commonly referred to as Sallie Mae. The sale price represents a nearly 50 percent premium for Sallie Mae’s previously sagging stock before takeover rumors emerged late last week.

Sallie Mae is by far the largest school lender, originating $23.4 billion in student loans last year, many of them federally subsidized such as widely used Stafford loans. Sallie Mae used to operate a loan center in Lawrence, Kan.