I have a little exercise for you.
Take 30 critics of education and give them each 30 1/4-inch diameter bolts with 20 threads per inch. From a mixed assortment of 1/4-inch nuts with 20 threads per inch and 28 threads per inch, give each critic 30 randomly-drawn nuts. Give them, say, 10-minutes each to put the nuts on the bolts. They will each be paid according to the number of bolt-nut pairs they can successfully assemble.
Knowledge is not bolts and students are not nuts. In fact, we tend to treat either the students who have difficulty absorbing the knowledge or the teachers who cannot match the knowledge to the students as dolts.
On a more practical level, consider a history teacher's task and a chemistry teacher's environment. If the school requires all students to take history but only a self-selected few students are going to take chemistry, which teacher do you think is more likely to have the better performance?
