It's no secret that low-birth-weight babies face significantly greater risks for certain health problems early on, such as respiratory distress or infection. Now, a new study from researchers at the University of Florida and Northwestern University shows that lower weights at birth also have an adverse effect on children's performance in school, which is likely due to the early health struggles small babies often face.

Using a unique set of data that matched birth and school records from 1.6 million children born in Florida between 1992 and 2002, the researchers found that the higher the weight at birth, the better children performed on reading and math tests in school. The findings held true throughout elementary school and into middle school regardless of the quality of the schools children attended.

These findings held true when socioeconomic and demographic factors were equal among children's families, said Jeffrey Roth, Ph.D., a research professor of pediatrics in the UF College of Medicine and a co-author of the study. But when socioeconomic factors and demographics are not equal, higher birth weights don't always translate to better performance in school.

For example, lower-birth-weight babies of highly educated parents tend to perform better in school than heavier babies of high school dropouts because the educational level of a child's mother is a stronger predictor of school success, Roth said. But when researchers compare children with similar family backgrounds, birth weight plays a key role in predicting future school success.

"We tend to think that good schools are places where struggling kids get special attention and motivated teachers can correct any problems with learning," he said. "This research indicates that is not always the case. Good schools are good for everyone, but even the best schools don't seem to differentially help kids with early health disadvantage."

For the study, Roth teamed with David Figlio, Ph.D., the Orrington Lunt professor of education and social policy and economics at Northwestern University, along with other Northwestern policy experts. The results were published in the journal The American Economic Review.

"This research agenda started when Jeffrey Roth and I were colleagues at the University of Florida," said Figlio, who previously served as the Knight-Ridder professor of economics at UF. "When education scholars are open to learning lessons from health scholars, and health scholars are open to learning lessons from education scholars, both fields advance."

Initially, the researchers examined data from twins only. Because twins face the same in-utero conditions and early life environment, studying how heavier and lighter twins fared in school offered researchers a natural set of socioeconomic and demographic controls so they could pinpoint the effect of birth weight on education. About 53 percent of twins were born at a low birth weight, meaning they weighed less than 5.5 pounds.

After examining the data on twins, the researchers compared their findings with the larger population of singleton births. Because singletons have more room to grow and are less likely to be born premature, only 5.9 percent of these children were born weighing less than 5.5 pounds. The researchers found the same patterns of birth weight's effect on school performance among both sets of children.

"Our results are remarkably consistent: Children with higher birth weight enter school with a cognitive advantage that appears to remain stable through the elementary and middle school years," the researchers write. "The estimated effects of low birth weight are present for children of highly educated and poorly educated parents alike, for children of both young and old mothers, and for children of all races and ethnicities, parental immigration status, parental marital status and other background characteristics."

The study is a result of a unique collaboration between the Florida Department of Health and the Florida Department of Education, which worked together to compile the data without compromising the privacy of the children.

"This study could not have been done without the willingness of these two large state agencies to collaborate," Roth said. "The DOE and DOH teamed up to create a very large de-identified data set to us to study. Florida is an exceptional place to conduct this kind of research."