The study is published in the journal Child Development.
Lead author of the study, Sara Gable, associate professor of nutrition and exercise physiology at the University of Missouri, Columbia, explained: "The findings illustrate the complexity of relations among children's weight status, social and emotional well-being, academics, and time."
The team examined more than 6,250 children from the Early Childhood Longitudinal Study-Kindergarten Cohort, who were followed from kindergarten to 5th grade. Throughout the follow-up period, teachers provided information of the children's interpersonal skills and emotional well being, children took academic tests and were weighed and measured, and parents provided information about their families.
The researchers found that children in the first grade performed worse on the math test if their obesity persisted from the start of kindergarten. According to the researchers, this lower performance continued through fifth grade. Girls who became obese between third or fifth grade also performed worse in math tests, although this poorer performance was temporary. For boys who became obese later, no such differences were found.
The team also found that poorer math performance among girls who were obese from the start of kindergarten may partially be due to their fewer social skills. For both genders who were persistently obese, feeling anxious, sadder and lonelier were also found to contribute to their poorer performance.
"Our study suggests that obesity in the early years of school, especially obesity that persists across the elementary grades, can harm children's social and emotional well-being and academic performance."