That's exactly what they say in the beginning: > First off, this is an observational study, not a randomized experiment. I think we may be reaching the limits

That's exactly what they say in the beginning: > First off, this is an observational study, not a randomized experiment. I think we may be reaching the limits of what analysis of observational data can do in the education debate and, given the importance and complexity of the questions, I don't understand why we aren't employing randomized trials to answer some of these questions once and for all.