Although, I agree that the public schools have a number of problems, not everyone would agree with the assumption that because kids aren't learning as well as they should be, that the schools are necessarily the ones who are most at fault.
I think a strong argument explaining the data you share can come back to issues with the larger society than with the schools per se.
Here is one example of someone who believes that in-home parenting may be a bigger influence on educational outcome than the school itself.
http://www.thelizlibrary.org/liz/parenting-and-educational-achievement.pdf In the primary age range the impact caused by different
levels of parental involvement is much bigger than differences
associated with variations in the quality of schools.
I have not done much research into this myself and I haven't checked their data. But I can say taht what I observe at DS's public school is that the teachers are excellent and class sizes reasonable. There is an excess of mandated testing and some odd curruculum choices made by the district. But in the end the real problem is that kids who don't have a home to go to at the end of the day, just aren't learning at the same rate as the ones who do. I find it hard to blame the teachers for that.
