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."
Re:A Randomized Controlled Trial of Interleaved Mathematics ...
by 0xab on Sunday May 19, 2019 @04:14PM
(#19955232)
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.
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."