I believe the second explanation is the likely cause, not differences in teacher effectiveness. This makes well known sociological sense since if you put a student who has more advanced knowledge into a class where that knowledge is just being retaught, that student effectively is being left back a year. In effect, there is a reversion to the mean effect here.

Contrary to the author’s statement that “there is no silver bullet in pre-K solutions”, quite the opposite conclusion is likely warranted since it is necessary to expand pre-K to universality so that the “lost year(s)” of the Head Start students in elementary school is not caused by the other (majority) students who have not yet attained Head Start standards before entering elementary school in the first place.

Of course, advocates of the teacher effectiveness model will try to use this research to further to limit pre-K expansion to universality. It is so sad to see this ideologically driven perspective continue to derail real educational reform in this country. But there is no way around it except to continue to fight the battle for Pre-K expansion.

Any familiarity with the research on the structure of scientific revolutions suggests that the teacher effectiveness model will eventually lose (although they appear to have temporary ascendency) for the simple reason that their reforms will never lead to the outcomes they expect or demand. It just does not touch the root of the problem. They will never change their minds of course, but if they have not yet effectively destroyed public education by that point, newer better educated generations will see that the Emperor has no clothes. And hopefully then, universal pre-K initiatives will eventually prevail, leaving many to wonder in the future why reformers in the past were so stubborn to institute what is so obvious.