A new study of elementary and middle school students has found that those who are the youngest in their grades score worse on standardized tests than their older classmates and are more likely to be prescribed stimulants for attention deficit hyperactivity disorder.
The findings suggest that in a given grade, students born at the end of the calendar year may be at a distinct disadvantage. Those perceived as having academic or behavioral problems may in fact be lagging simply as a result of being forced to compete with classmates almost a full year older than them. For a child as young as 5, a span of one year can account for 20 percent of the child’s age, potentially making him or her appear significantly less mature than older classmates.
The new study found that the lower the grade, the greater the disparity. For children in the fourth grade, the researchers found that those in the youngest third of their class had an 80 to 90 percent increased risk of scoring in the lowest decile on standardized tests. They were also 50 percent more likely than the oldest third of their classmates to be prescribed stimulants for A.D.H.D. The differences diminished somewhat over time, the researchers found, but continued at least through the seventh grade.
The new study, published in the journal Pediatrics, used data from Iceland, where health and academic measures are tracked nationally and stimulant prescription rates are high and on par with rates in the United States. Previous studies carried out there and in other countries have shown similar patterns, even among college students.
Helga Zoega, the lead author of the study, said she had expected there would be performance differences between students in the youngest grades, but she did not know that the differences, including the disparity in stimulant prescribing rates, would continue over time.
“We were surprised to see that,” said Dr. Zoega, a postdoctoral fellow at the Mount Sinai School of Medicine in New York and an assistant professor at the University of Iceland. “It may be that the youngest kids in class are just acting according to their age. But their behavior is thought of as symptoms of something else, rather than maturity.”
In the study, Dr. Zoega and her colleagues tracked over 10,000 students born in Iceland in the mid-1990s, following them from fourth through seventh grade, or roughly ages 9 to 12. Iceland has detailed national registries containing health and academic information, so the researchers were able to compare students’ scores on standardized tests and look at the medications prescribed to them.
The researchers then divided the subjects based on the months in which they were born. In Iceland, children start school in September of the calendar year in which they turn 6, and the nationwide birthday cutoff in schools is Jan. 1. So the oldest third in any grade are born between January and April. The middle third are born between May and August, and the youngest third are born between September and December.
The study showed that average test scores in mathematics and language arts, which covers grammar, literature and writing, were lowest among the youngest students in each class. On standardized tests at age 9, the children that made up the youngest third ranked, on average, about 11 percentile points lower in math and roughly 10 percentile points lower in language arts than their classmates who made up the oldest third. Compared to the oldest students, the younger ones were 90 percent more likely to earn low test scores in math and 80 percent more likely to receive low test scores in language arts. By the seventh grade, the risk had diminished somewhat, but the younger children were still 60 percent more likely to receive low test scores in both subjects.
A similar pattern was seen with A.D.H.D. medication, with students in the youngest third of their grade significantly more likely to receive stimulant prescriptions than their classmates in the oldest third. Dr. Zoega found that gender had some influence as well. Over all, girls scored higher than boys on tests, and had lower rates of stimulant prescriptions. But ultimately there was still an age effect among girls for both academic performance and the use of A.D.H.D. medication.
The findings dovetail with research carried out by two economists, Kelly Bedard and Elizabeth Dhuey. In looking at fourth graders around the world, the two found that the oldest children scored up to 12 percentile points higher than the youngest children. Their work, which was described in the best-selling 2008 book “Outliers” by Malcolm Gladwell, has shown a similar pattern among college students.
“At four-year colleges in the United States,” Mr. Gladwell wrote, “students belonging to the relatively youngest group in their class are underrepresented by about 11.6 percent. That initial difference in maturity doesn’t go away with time. It persists. And for thousands of students, that initial disadvantage is the difference between going to college — and having a real shot at the middle class — and not.”
Dr. Zoega said she did not want her study to be seen as an indictment against stimulants. Instead, parents and educators should consider a child’s age relative to his or her classmates when looking at poor grades and at any behavioral problems.
“Don’t jump to conclusions when deciding whether a child has A.D.H.D.,” she said. “It could be the maturity level. Keep in mind that he or she might not be performing as well as the older kids in the class, and that should not be a surprise.”