Actually, again I realized in some sense this has already been studied here.
According to this interesting ongoing series:
31% is right around the same percentage of Oxbridge interviewees who actually get admitted, and then presumably these 40 feeder high schools have at least some idea which of their students are more likely to be in that 31%. So that is at least the same, and probably more, predictability for their graduates to those 12 schools as Oxbridge offer–for applicants like that.
The study goes on to show the most popular alternatives were other selective private universities like NYU, Georgetown, Tufts, USC and WashU, public universities like UMich, UVA, UC Berkeley, St Andrews (UK), and UW, and LACs like Wesleyan, Bowdoin, Middlebury, Colby and Amherst.
So this also helps demonstrate that for this sort of US college population, the “second choice” sorts of colleges (which might actually be first choices for some kids–plenty of our kids would prefer some of those schools to at least some of the Ivies, say) tend to be exactly what you would expect.
OK, so for these kids, college admissions does not in fact seem notably more unpredictable to me than in, say, the UK, Canada, and so on.
Which is not all kids in the US, of course. And that is probably the more interesting discussion, which kids are getting more certainty in highly selective US college admissions, and why.
And of course it is also tying into another long-standing discussion–if “diversity” in highly selective US college admissions is mostly just about sorting out which of these kids ends up exactly where among these colleges, is that really what people have in mind when they think about diversity?
Edit: I realized this chart is linkable, so . . .
Northeastern did appear on the list! In fact there were a total of 5 not-top-40 privates on the top 39 list, Northeastern, Tulane, BU, SMU, and Wake Forest.
I don’t personally think it is a big mystery why. Based on where these sorts of kids have already chosen to go to high school, it makes sense those would be the sorts of colleges they might choose absent an even more aligned option.