That’s not at all what the article claims. It presents a hypothetical scenario, based on real SAT average scores, where somebody can reach a very wrong conclusion (teacher unions are bad) based on this data. Then the article proceeds to explain how the difference in the average scores can be attributed to self-selection among students who take the SAT rather than unions. So, the article not only remarks on the suspicious causality but the suspicious causality is the article’s main point.
I understand what you are saying, but really don't think that suspicious causality is what the article is about at all. It's about selection bias. (not the same as causality)
Indeed after reading the article I feel it is generally well written and compelling. However the contrived teacher union scenario is a big distraction for me as I was reading the article hoping that issue would be addressed and it wasn't. It would have been much stronger without this gaping logic hole introduced in the beginning.
