One of the issues with the original survey is that the data is reported by elementary school district, and the method for determining schools districts is not consistent for the entire country. For example, Illinois has a number of very highly ranked districts and very poorly ranked districts. In Illinois, the boundaries for elementary districts are based on townships, so there are a great many small districts reported. Look up Winnetka Ill. 36. This is a very small elementary school district in northern Cook County with median income levels of $222,000 which is 2.5 times the grade level. It is one of the best performing districts in the country.
However, other states like Florida report the information for elementary schools on a county level, so the big disparities in income and achievement levels like you see in states like Illinois and Massachusetts don’t show up.