[001sky]

In a pure meritocracy, the best academic students are admitted, since college has an academic purpose. Most of these academically-oriented students are going to be the driven-to-succeed type. It benefits a school not at all to have an unhappy bottom quarter who feel driven to succeed yet are outclassed academically by the rest of the cohort. However, it's impossible to help the bottom quarter in general because there always must be a bottom quarter by definition.

Instead, pioneered by Harvard, the "Happy Bottom Quarter" philosophy argues that for the sake of fundraising, reputation, and the self-esteem of students, schools should admit people specifically for the bottom quarter[1]

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[1] http://www.quora.com/College-and-University-Admissions/What-...

[apologies on the source, but it's footnotes are researched and worth the correct attribution].