[SWTXBelle]

The private school at which I taught had a very comprehensive English program. The junior year incorporated a great deal of what I taught in college English 1301, and the senior year incorporated what I taught in 1302 (I even used college texts). Most of them went on to be exempted from freshmen English classes by virtue of the AP or their verbal score - and this is at schools ranging from U of Chicago, Yale, Penn, Stanford, you get the picture. Many of them got extra money helping students in their dorms with their papers!
But we had the luxury of designing our own curriculum - here in Texas you have to use "approved" texts for public schools, and the selection process can be very political. Even the most brilliant of public school teachers will have their hands tied by various curriculm and administrative requirements. That doesn't mean that there isn't quality instruction going on - it just means it can be difficult to jump through the hoops.
Another factor, I feel, is that when I graduated with a B.A. in English I had TWICE as many English credits as someone who graduated with an Education degree with an English emphasis.
There are a multitude of reasons why many public school students do not graduate with what I would consider acceptable reading and writing skills. One of my former students reported back from Baylor that when asked what their favorite novel they had read in high school was, all of the Houston ISD students reported that they had not read any - just short stories. Teachers with crushing class loads are simply not going to be able to require the kind of work most students need to hone their skills.
I do think the situation may be getting better - I have three 1302 courses to teach in the fall, so I'll let you know. The essay portions of the ACT and SAT should, at the very least, let colleges know which students are weaker.
If I had my druthers, I'd require students who were weak in English skills to take remedial classes at their local community/junior classes the summer before their freshman year.

eta - My alma mater has a Writing Center to help with "Writing across the Curriculum" - a program that incorporates writing in ALL academic disciplines. The idea is that any graduate of Texas State will be a competent writer.