School districts nationwide have been removing sugary drinks and junk food from campuses, and those measures may be working to reduce obesity in schools.

But studies suggest youngsters may be most likely to pack on pounds when they are home for summer vacation.

For a study in The American Journal of Public Health, researchers tracked 5,380 children through kindergarten and first grade at 310 schools. They found that body mass index (BMI) accelerated at a faster rate during summer vacation than during the school year. The researchers speculated that children put on weight more quickly during summer for reasons that might also explain why adults gain weight faster during the holidays.

“Many nonschool environments are relatively unstructured and unsupervised,” researchers wrote, “allowing children to indulge in sedentary activities and excessive snacking.”

Although schools are a factor in childhood obesity, they added: “It appears that they are healthier than most children’s nonschool environments.”

Perhaps healthful policies in school, researchers wrote, should address the summer as well.