Bit of anecdotal evidence: I came from a shitty (teachers as babysitters, no metal detectors though) high school, with respectable (760/760) SAT scores. I went to community college for health reasons and later transfered to UCLA. Health aside, I’m very glad to have had the transition time at the CC. The level of writing (and hell, pretty much all things academic) taught even at the honors level in a subpar high school does NOT adequately prepare one for a high-end university.