Just another thought to your point Wren - to some degree, it's possible that exposure to these classes *is* the intervention. For HS students aiming for university, they may well have the metacognitive skills (or supports) to identify gaps and work on them again in other coursework. Striving in the ZPD is healthy and motivating.

It would be fascinating to run this program longitudinally to track whether the class itself is a treatment.

What is to give light must endure burning.