Interesting discussion. I read the paper (thanks to Dynarski for the link).
A few questions to the authors if they are following this discussion. It would be great to hear their comments:
1. The study doesn't address the most important question to me as a parent: what is the optimal age to begin academic education? The Scandinavian countries like Norway start at 7 (two years, not one year, later than we do) and they clean our clocks. The educational attainment of kids in those countries is much, much higher than in the US. This suggests that the link you suggest between being older when you start school, and later adverse impacts, has nothing to do with age per se.
2. The study seems to posit, at most, an apparent correlation between the 'graying' of kindergarten and declining results and rising drop out rates. But I don't see why there is a necessary causal relationship. There are so many things that have changed in the last 40 years. The correlation you posit seems rather crude.
3. If the problem has nothing to do with age per se (see #1), what is driving the problem? Any parent who has had experience with the educational system a northern, continental European country and even an affluent 'high performing" public school district in the US knows how poorly ours compare. Could it be that our kids are doing poorly because even our best schools stink, relatively speaking?
4. I assume that high school drop out rates correlate to socioeconomic status. It is very, very hard to believe that the upper middle class cohort of 'redshirters' are really doing worse at the end of the game. Do you have any data broken down by socioeconomic class?
5. If starting school later is such an economic hardship for working class parents, I would expect those kids to start earlier. But you seem to suggest that everyone is starting later. Why would that be? It doesn't make sense. Could it be that the social dynamics behind later starts for kids varies by economic/social class, and that an aggregate analysis is really not very meaningful?
