A wide-ranging study of pedagogy could bring about revolutionary advances in education, much as similar studies have brought about changes in medicine, as Gawande documents. Instead, nearly all efforts go into producing yet more new methods.
Why?
I run a small business producing educational materials, so I know well why: No one makes money testing existing procedures (outside of the politically-connected testers, of course, but innovators need not apply), nor by making incremental changes over a generation, even if those incremental changes amount to tremendous benefit to students.