Should Children Redshirt Kindergarten?

Every September, the class of incoming American kindergartners is ever slightly older.

In the U.S., kids who start kindergarten must be at least 5 years old. In theory, that seems like a clear-cut, easy enough rule─like the "You must be this tall to go on this ride" sign at an amusement park. But what's driving the trend toward an older kindergarten class is the increasing number of 6-year-old "redshirted" kids whose parents have delayed their entry.

In 1980, about 10 percent of kindergartners were redshirted. Since then, the proportion has doubled.

It seems that fewer parents are comfortable with their child being one of the youngest in the class, the runts of the litter. By simply holding them back, parents can ensure their child begins the rat race as one of the oldest, most mature kids in class.

It's not surprising that the older kindergartners, on average, are slightly better students when they begin school. The real question is, does that initial age advantage last, or does it quickly peter out?

Until now, the research everyone looked to was by UC Santa Barbara's Kathy Bedard and Elizabeth Dhuey. Bedard and Dhuey gathered achievement data in theU.S. andEurope, comparing the youngest kids in class with those months older. In fourth grade, the older kids were still performing a few percentage points better. In eighth grade, the advantage persisted; depending on the method of calculation, the oldest kids in eighth grade in the U.S. were ranking 4 to 8 percent higher than the youngest children in that grade.

The Bedard study became exhibit A for parents considering redshirting─even more so after Elizabeth Weil addressed it a New York Times Magazine article and Malcolm Gladwell discussed it in Outliers. By their interpretation of the data, if you wanted your child to be seen by teachers as one of the best students in class, and eventually win entrance into the best high schools, redshirting was a logical option to ponder.

Now two recent studies may completely flip the redshirt argument on its head.

First, scholars from National Bureau of Economic Research─Kasey Buckley and Daniel M. Hungerman─recently looked at detailed data from the birth certificate of every single child born in the United States from 1989 to 2001.

Astonishingly, they discovered slight differences in the seasons of the year that poor women and wealthy women give birth. The scholars couldn't answer exactly why this was the case. It could be the accidental effect of differing work and vacation schedules, so that more affluent mothers get pregnant over the Christmas holidays, while more poor women get pregnant in the late spring and summer. Or it could be a conscious decision─perhaps some well-educated moms are timing their births, either to ensure their child is older, or to avoid caring for a newborn in the hot summer. But the seasonal patterns were clear in every year of the data.

So it turns out those fourth and eighth graders aren't doing better just because they're a few months older. They're doing better because more of them are born to mothers who are affluent, college-educated, married, and white.

Combined, the seasonal birth pattern explains at least half the achievement gap between the oldest and youngest kids in class. That 4-point advantage is more like a 2-point advantage.

Second, a soon-to-be-published study by Todd Elder and Darren H. Lubotsky has debunked the theory of why older kids do better. It used to be argued that older kindergartners can soak up more from their teachers, learning at a faster rate. Each school year, this tiny advantage compounds. Like the NBER team, Elder and Lubotsky found the driving variable wasn't how old the kids were, but how prepared the kids were by their preschool, day care, and home environment. The better-prepared kids learned more.

Elder and Lubotsky couldn't find any merit in redshirting─waiting a year to educate a child. Because what is more of an enriching intellectual experience for a child than going to school? "Our estimates clearly indicate that children's reading and math abilities increase much more quickly once they begin kindergarten than they would have increased during the same time period if they delayed kindergarten entry," the scholars wrote.

So that's the choice parents face: is a 2-point statistical advantage worth having a child sit on the sidelines of learning for a whole year?