Stop Cheerleading Education Miracles, i.e. Education Effects Are Small
“We really have failed in the teaching of mathematics and probability,” decries Baker, who regularly debunks myths about unicorn policy changes that radically improve student outcomes. At scale, experiments rarely move the needle more than a few percentage points. Statisticians measure outcomes in “standard deviations”, or how students move relative to their peers.
I've added his blog to my RSS reader. Unfortunately, it seems that for policy makers the only data that is good is data that confirms their own beliefs.