[UPDATE February 2015: Over the past few years, numerous people have commented on my last paragraph as being an overstated and overheated conclusion, unwarranted by the data and of no help in advancing reform. Fair enough: I have come to think that they are correct. So, a new concluding comment is attached, with the old concluding paragraph available for inspection. I agree with my critics: there is no need to pile on teachers in this era of teacher-bashing – and it was not my point. My point was to say: we can improve learning, so let’s do it.]

[UPDATE 11/2014: There have been recent reports suggesting that some of Hattie’s math is flawed. I am not in a position yet to judge the validity of the critique nor, perhaps more importantly, to determine the impact of that critique on the overall findings. The author of the statistics critique in fact suggests that…