Teaching

From an article about training teachers:

Eric Hanushek, an economist at Stanford University, has estimated that during an academic year pupils taught by teachers at the 90th percentile for effectiveness learn 1.5 years’ worth of material. Those taught by teachers at the 10th percentile learn half a year’s worth. Similar results have been found in countries from Britain to Ecuador. “No other attribute of schools comes close to having this much influence on student achievement,” he says.
Rich families find it easier to compensate for bad teachers, so good teaching helps poor kids the most.

It is hard for me to imagine why that would be true.  He adds that if the average American teacher were as good as those at the top quartile the gap in test scores between America and Asian countries would be closed within four years. The above is also hard to believe does he assume a cumulative effect without diminishing returns?  

I had some bad teachers but I doubt that better teachers back then would make me smarter or significantly more knowledgeable now. I think that the low hanging fruit in schooling is to focus on what is taught, teaching the most important stuff, rather than trying to get students to learn more. Most of what is taught currently is only a signal for further schooling. Case in point the article seems to imply that in 4 years of college teachers are not taught how to teach! And that Ed majors are not flunked out if they do not show good ability to teach before graduation! That is alarming!

The article is self refuting. If schooling is signalling then the raising the quality of all teachers will have little/no impact, but if schooling is about human capital formation, how is it that after 4 years of college focused on teaching, teachers have not taught bee adequately taught how to teach! That Ed majors are not flunked out if they do not show good ability to teach before graduation would be considered alarming if college were about human capital formation! It would seem that that fact would be devastating to the human capital formation theory of schooling.