TUESDAY, April 24 (HealthDay News) -- Even first-graders might be shunned by their peers if they are overweight or obese, new research suggests.

In the study, first-graders at 29 different schools in rural Oklahoma rated how much they liked to play with each of their classmates. Children who were overweight and obese scored significantly worse than thin students.

"This is striking to me because these are just little kids," said study author Amanda Harrist, an associate professor of human development and family science at Oklahoma State University. "I think this might be one reason that kids in elementary school that are obese avoid school, and it could exacerbate their weight problem" because they are less likely to play and get exercise, she added.

The research is scheduled to be presented Tuesday at the Experimental Biology meeting in San Diego.

About 17 percent of children and teens in the United States are obese, and one in three children under the age of 5 is obese or overweight, according to the U.S. Centers for Disease Control and Prevention.

With overweight and obesity becoming so common among children, it might stand to reason that acceptance may also be increasing. But, a previous study suggested that obese children are actually more disliked now than they were several decades ago.

In the current study, researchers surveyed 1,139 students whose average age was 6. They showed each student a photo of their classmates and asked them to say how much they liked playing with them on a scale of one to three.

More than one-third of the children in the study were overweight, or had a body mass index (BMI) in the top 15 percent for their age and sex, and 16 percent of the children were obese, meaning they had a BMI in the top 5 percent for their age and sex.

"This study shows that not only is [discrimination] starting really early, but the consequences are very likely starting early as well," said Rebecca Puhl, director of research at the Rudd Center for Food Policy and Obesity at Yale University.

"This leads to a range of negative psychological consequences -- higher depression, anxiety, suicidal thoughts, and a lot of times kids who are getting teased about their weight turn to unhealthy eating behaviors and avoid physical activity," Puhl explained.

It is possible that the overweight children in the study acted differently than their thin counterparts, and that it was their behavior rather than their weight that made them less popular, Harrist noted. If children are unhappy, they might be less friendly toward others and also more likely to overeat, she added.

In their surveys, Harrist and her colleagues asked children about each classmate's conduct, such as whether they got mad easily. The group is now analyzing those data to see if behavioral problems are associated with being overweight and being less popular.

The researchers also asked the teachers of the classes in their study to estimate how well they thought each student was liked. The teachers' estimates matched the student ratings, and were similarly associated with weight, indicating that the teachers were tuned in to which kids were accepted.

Teachers could be the best defense against weight stigma, Harrist said. She and her colleagues are developing a curriculum based on the message that every kid should be able to play and targeting peer relations in addition to diet and exercise.

"Intervention and prevention efforts have to start early. You don't want to wait until sixth-grade," Harrist said.

And intervention efforts have to reach all schools, Puhl pointed out. Her research has found that teachers in rural settings are less likely to step in than their city counterparts, perhaps because policies are different or bullying is more rampant in urban schools.

Even worse, teachers themselves have been found to have prejudices against overweight students. Special training for teachers to help them understand the complexity of weight problems might be in order, similar to the training that health care workers, another group with known weight biases, receive, Puhl said.

The findings were presented at a medical meeting and should be considered preliminary until published in a peer-reviewed journal. The study was funded by the U.S. Department of Agriculture.

More information

To learn more about weight discrimination, visit the National Association to Advance Fat Acceptance.