As I understand it, private educational institutions are exempt from the 14th amendment - see Wellesley and other women's colleges, and all the single-sex prep schools. In one interesting case, a religious university lost its tax-exempt status for enforcing a no-interracial-dating policy (http://www.phschool.com/atschool/ss_web_codes/supreme_court_...) but nobody said that they couldn't discriminate and still be a university.