Teddy Roosevelt built some of his reputation on trust-busting--breaking up monopolies or alliances that controlled large sectors of the economy. At least since that time, Americans have had a healthy skepticism about too much alignment in a sector.
Perhaps that (and more seriously the history of local control of public education) has something to do with why public schools and public universities have such a hard time aligning their curricula and systems so that a student who graduates from high school can succeed in higher education. It is true that there is some effort to align curricula in some states, and a bit of overlap in administrative systems, but truth be told, creating K-16 alliances in public systems still looks like a pipe dream.
But why not try it in private education? After all, private schools trumpet the distinctiveness of their educational models--small classes, focus on active learning, etc., etc. And then they bewail the fact that many students coming out of public schools aren't prepared for their approach to learning. So why not vertically integrate?
There could be two models for doing this. The simplest would be to create alliances with high schools (public or private) where the college guarantees admission slots (say 10/year) to students who the high school deems to be best prepared to succeed in that particular college. The college and the high school would work together to make sure expectations are aligned, but in the end the high schools would pick enrollees, and those students would go, together, to college. (The Posse Foundation does this a bit, making it possible for groups of students from underserved populations to attend the same college together, creating a ready-made community for them.)
The more radical approach would be to create an entire K-16 system under the same private umbrella. Here, if they choose to do so, students would take an entire primary, secondary, and tertiary education in the same system. College would be a natural result of graduating high school. College faculty would have a clear idea of the strengths and weaknesses of their students; and students would know clearly what to expect. And the system, by attending to its outcomes, would be able to say with a greater level of certainty whether or not its approach to education does what it promises.
Such systems, in a much less formal fashion existed among religious communities in the 19th century. But the secularization of higher ed, the expansion of the public school system, and the divergent purposes of K-12 and HE made those older systems collapse. Perhaps good riddance. Or perhaps we have lost a model that would serve some institutions, some schools, and some students well today.