A better way to measure school performance

We all want our kids and grandkids to have the best education possible, but it is very hard to measure the effectiveness of a school system. We can look at per-pupil spending, but there’s no shortage of inefficient systems that spend a lot of money. The student-teacher ratio is also easy to measure, but it often doesn’t correlate with good test results.

So we usually look at standardized test results, but these are confounded by the socio-economic status of the students taking the test. Years of measurements have shown that children from lower socio-economic backgrounds will, on average, score lower than children from higher socio-economic backgrounds, no matter how good their schools...