The Manhattan Institute created a Teachability Index from 16 social, economic and demographic characteristics, which measures the difficulty of educating students. It finds that student disadvantages have declined 8.7 percent since 1970 (spending has, of course, gone up and performance down) Hmmm, so what's the solution?
The study also evaluates the performance of schools in each state once the difficulty of teaching that state’s student population is taken into account. By empirically measuring the difficulty of educating each state’s student population, this study offers the first fair comparison of the test score performances of state school systems. States with school choice or strong accountability testing performed significantly better once differences in student disadvantages are taken into account.