One possibility is a system of national exams, sponsored by employers, that would allow students from less prestigious schools to demonstrate that they had learned as much as or more than Ivy grads. As it stands, the top companies companies tend to recruit only at the top schools, so it is difficult for students from West Texas University or California State Chico to demonstrate their qualifications. Hundreds of companies use university prestige as an imperfect proxy for intellectual ability.
Needless to say, this system is deeply unfair. Whether or not someone impressed an admissions committee at age 17 (and admission committees are imbued with the usual higher education pieties and prejudices) is hardly the best way to measure what he or she has learned by age 22. People mature in different ways and at different paces, and use their time in college differently as well. Since it can be hard to perform poorly at grade inflation mills like Harvard, especially in the soft subjects, almost everybody who gets in graduates—no matter how little they learn.