Ok . . . so I taught in public school for forty years and am developing a pity for Hattie having wasted his life on crunching numbers that basically add up to zero.
You can critique Hattie's work right from his initial claim 98% of things work, e.g his main Feedback study Kluger &DeNisi report more than 38% of feedback does not work! Marzano says about 40% of things don't work. Then there is the file drawer problem, which is a bias toward studies that work, ones that don't work are not published but put in a file drawer. There is a lot of peer review critique of Hattie's work, teacher's need to be aware of this, I've summarised here - visablelearning.blogspot.com/
