This does not mean that redshirting upper-middle-class kids turns them into high-school drop-outs. Deming and Dynarski show that in 1968, 96 percent of 6-year-olds were enrolled in first grade or higher. In 2005, the rate was 84 percent. (Forget about skipping a grade—that went out at least a generation ago.) Redshirting explains two-thirds of the change, the authors find, and changes in state laws explain the rest. The kids who start later because of the legal changes—a group that is socio-economically broad—are probably fueling the second trend that Deming and Dynarski point to: fewer 17-year-olds in 12th grade or in college, which translates to fewer years of school for more kids. Laws in the United States (as opposed to some European countries) mandate that kids stay in school, not for a requisite number of years but until they are 18. "Poor kids are disproportionately likely to drop out as soon as they can, when they turn 18," Dynarski explains. "If they start at 6 instead of 5, that's one year less of school."
The increasing availability of public pre-K becomes, then, not the additional year of school that early childhood educators and advocates wanted for families that can't afford private preschool. Instead, pre-K, when it's offered, just replaces what the first year of kindergarten used to be.
One more knock against delaying kindergarten: It doesn't produce better test scores over the long run. If this delay did help, we could expect to see a cheery rise in the scores of 17-year-olds along with the rise in the number of 6-year-old kindergartners. Instead, the basic level of proficiency of 17-year-olds on the National Assessment of Education Progress "has not risen at a rate that would suggest the majority of students are learning at a grade level higher than they were 20 years ago," Deming and Dynarski write.
All of this should make us leery of governmental policies that delay kindergarten. But back to your kid, because, well, he's yours. He's little. And immature. He could be the kid who won't sit on the rug for reading time or the one who will cling to his mother's leg. Won't he be better off if he waits?
Deming and Dynarski do their best to argue no. "There is no evidence of a lasting benefit to education or earnings from being older than one's classmates," they write. Another recent study, by Sandra Black of UCLA, crunched data from Norway and actually found a small boost in IQ for starting school early, but little effect on educational attainment—how well kids do in school in the long run. The place where redshirting is a proven advantage is the sports field. For example, 60 percent more Major League Baseball players are born in August than in July, and the birthday cutoff for youth baseball is July 31. But athletics, Dynarski points out, isn't academics.
No evidence of a lasting redshirting benefit, though, isn't the same as convincing evidence of no benefit. What a lot of parents really want to know is whether redshirting improves a kid's chances of grabbing the brass ring—admission to an elite college. Deming and Dynarski say they are "exploring whether age effects persist in this competitive arena." Those are the kind of research results that will interest parents who can afford to choose between another year of preschool and kindergarten. For the sake of parents who can't, it would be better if the perceived advantages of redshirting lose their shine.