At our county community college, outside DC, about 25% of the students have to take remedial math and English. It's not that these students aren't ready for college. It's that they really weren't ready to graduate from high school. The 60% of the students who do graduate have 7th grade math and 9th grade reading skills. Having these guys go to a JC doesn't solve any problem, but it is cheaper to patch them up at our CC than a more expensive 4-year school.
I believe though that it does dramatically increase their chance of success when they do then go to the four year school.