CHAMPAIGN, Ill. — New research challenges a growing trend toward holding kids out of kindergarten until they're older, arguing that academic advantages are short-lived and come at the expense of delaying entry into the workforce and other costs.
The findings show older kindergartners fare better academically largely because they learn more before starting school, not because age improves aptitude, said Darren Lubotsky, a University of Illinois economics professor who co-wrote the study.
Older students post higher test scores than younger peers during the first few months of kindergarten, but their edge soon fades and nearly vanishes by eighth grade, according to the study, which will appear in the Journal of Human Resources.
"If it were true that older kids are able to learn at a faster rate, then the differences in test scores should get bigger as kids progress and the material gets more difficult. But we really see the opposite," Lubotsky said.
The findings counter decades of research linking age to academic achievement that has led states to push back kindergarten entrance age deadlines and convinced more parents to start children later than the once-traditional age of 5.
In 2002, nearly 21 percent of 5-year-olds were not yet enrolled in kindergarten, up from less than 10 percent in 1980, according to the study, co-written by former U. of I. economist Todd Elder, now a professor at Michigan State University.
Though older students have an early edge based on an extra year of skill development, the study maintains that older and younger students learn at the same pace once they enter school, based on a review of federal education data.
The study found, for example, that older kindergartners scored 24 percentage points higher than younger peers on standardized reading tests, but the gap narrowed to less than 4 percentage points by eighth grade.
"Kids learn at lot before kindergarten, especially if they're in preschool. One way to think about it is that the oldest kid in kindergarten has about 20 percent more life experience," Lubotsky said. "But once they start, they basically learn at the same rate."
Based on the findings, Lubotsky says parents and lawmakers need to weigh costs and benefits as they consider when to start kids in kindergarten.
"Older kids may do better at first, but there's a tradeoff," he said. "They're also a year in school behind other kids their own age. At the end of the line, somehow that year will catch up to them. They start work a year later, and parents have an extra year of child-care costs if they delay entry. So it's not free."
Lubotsky says the study also found that wide age gaps caused by holding kids back from kindergarten have both positive and negative effects on younger students.
On one hand, younger students tend to score higher on tests when they have older classmates, who may help tutor their peers or simply set higher standards that others seek to achieve, Lubotsky said.
But the study also found that having older classmates makes it more likely that younger peers will be held back or diagnosed with learning disorders such as attention deficit disorder.
"What we think is going on is that teachers are comparing younger kids to older classmates and the younger kids tend to stand out," Lubotsky said. "They stand out either as not doing as well or they tend to stand out as being more hyperactive."
"Older kids do better at first and younger kids do worse, but they catch up," he said. "The thing is schools are making profound decisions based on these differences – differences that tend to fade away."
Lubotsky says follow-up research is planned to determine whether the academic advantages of age continue to decline through high school.
"It's clear the pattern is these academic differences get smaller as kids get older," he said. "It doesn't seem reasonable to us that there could be large long-term gains from starting kindergarten at an older age when there isn't much of an effect for kids in eighth grade."
Lubotsky says parents still need to weigh children's needs and consider holding them back if they are immature, can't sit still in class or have other issues that could affect learning. But he says the study's bottom line is that kids are generally best served by starting school as early as possible.
"Kids get so much more out of just learning," he said. "Whether they go to school earlier or later, that's really not going to matter much at the end of the day."