Hacker News Reader

I am affraid this might be https://en.wikipedia.org/wiki/Hawthorne_effect

I don't see anything controlling for that in the setup:

"The present study examined interleaved practice in a large number of classes at multiple schools over a period of five months, and all instruction was delivered solely by teachers who had no prior association with the intervention or the authors."

View on HN

There's a control group. Both groups were watched by the experimenters. Not only that, the same teachers had students in both groups in different classes.

But the control group would know that nothing has changed. The group testing the new method would feel the excitement - the control group would not.

Reply on news.ycombinator.com