(Guest Post by Matthew Ladner)
So to get into this chart you had to have a NAEP math score for your charter sector in the 2011 4th grade test, and then again for 8th graders in 2015. Many states either have no charter schools at all, or too few charter schools in 2011 (NC for example), or too few charter schools in 2011 or 2015 to make either sample. Some states fell into this lattercategory despite having venerable charter laws (yes I’m looking at you Indiana and Nevada). If you don’t see your state on the chart, keep calm and open more charter schools.
Otherwise a few notes: Pennsylvania and Maryland both look to have accidentally forgot their charter students any math between 4th grade in 2011 and 8th grade in 2015. I mean there is a few points of gain but one would expect that simply through aging. There might be something odd going on with the sampling or inclusion standards, but if I lived there, I’d be anxious to get to the bottom of it. I don’t so I’m not.
Michigan had the same progress over time as Louisiana despite the fact that Louisiana has been supported with philanthropy and TFA kids to a much larger extent.
Arizona and Colorado are sitting on the bench in the second half eating hot dogs and watching their backups brutalize their hapless opponents.
Jay P. Greene's Blog 
On this chart, the vertical axis is what we really care about, right? I mean, why praise CO and not MN when MN made more gains?
Pondiscio convinced me that both are important, but I agree that MN is the one state that seems to have done well despite having a high NACSA score.
The one state? AZ seems to have made equally large gains starting from an even higher score. Not like you to sell AZ short! Or is AZ so good that it no longer even counts?
No AZ is blessed with a low NACSA score…
Ah, didn’t track with you there, sorry.