“6 years is 150% of the nominal time for a bachelor’s degree; it seems to be the usual method for measuring whether someone is likely to complete the degree at all.”
I think many of the engineering programs encourage or require co-ops which usually means that the students graduate in 4.5 or 5 years, so looking at 6-year seems fair, and for a lot of other reasons as well.
"I look at colleges with student bodies heavily slanted towards kids from privileged backgrounds and wonder why they aren’t graduating everyone in 6-8 years… "
Those colleges do pretty well wrt grad rates, most in the 90s. I just googled Harvard and one site said of the 1600-1700 entering freshman a few years back, 33 didn’t graduate in 6 years, of those, half transferred, a few are still there, the rest they assumed dropped out.
"Theoretically, if all things are equal all races would produce the same percentage of what you call “college ready” students, of top-percentage students, and of low-performing students.:
I don’t know if that’s going to happen, CA may be worse than Louisiana in terms of achievement gaps based on ACT, 73% of Asians are college ready, 71% whites, 26% Latino, 24% black.
"And theoretically, all public colleges in those states would have demographic percentages that match the percentages of their K-12 enrollments. "
That seems like a reasonable goal, if you include all public colleges, so in CA, it would be UCs, CSU and Cal Polys, maybe even the community colleges. I believe some of the recent data show Latinos being the largest ethnic group and in CA, in the 2019 hs class for the UCs, Latinos were the second largest group behind Asians.