Lead author Jennifer Van Hook of the Pennsylvania State University and Claire E. Altman, a sociology and demography doctoral student at the same university, used a sub-sample of 19,450 children, in fifth and eighth grades in the 2003-2004 and 2006-2007 school years.
The study, published in the Sociology of Education, found 59 percent of fifth graders and 86.3 percent of eighth graders involved in the study attended schools that sold junk food.
While there was a significant increase in the percentage of students between fifth and eighth grades who attended schools that sold junk food, there was no rise in the percentage of students who were overweight or obese.
Despite the increased availability of junk food, the percentage of students who were overweight or obese decreased from 39.1 percent in fifth grade to 35.4 percent in eighth grade, the researchers said.
"We were really surprised by that result," Van Hook said in a statement. "Schools only represent a small portion of children's food environment. They can get food at home, in their neighborhoods and they can go across the street to buy food. Additionally, kids are actually very busy at school. There really isn't a lot of opportunity for children to eat while they're in school, or at least eat endlessly, compared to when they're at home."