The new study, which examined the consumption habits of around 1,500 students in 10 different middle schools, revealed that 71 percent of the children purchased sugar-sweetened beverages from school vending machines.
And although schools are not the only place where children have access to drinks such as soda, fruit drinks and iced tea, because of their "broad reach" , it is important to focus on schools as a primary and practical means for reducing added sugar intake, said the researchers.
The new report adds to the growing evidence condemning the use of vending machines in schools, or the low-nutrient content of the products available in these. Indeed, the mounting criticism has resulted in a growing number of state legislatures considering bills that would limit soft drink availability in schools.
As of April last year, 28 states had made efforts to restrict sales of competitive foods, or products that are not part of the US Department of Agriculture's school meals programs. The percentage of school districts that reported having a policy that removes carbonated beverages from vending machines is up to 38 percent, from 18 percent last year, and is likely to grow further.
These attacks on soft drinks as a primary cause of childhood obesity have not come without an equal marketing push from beverage giants.
The largest soda manufacturers - Coca-cola, PepsiCo and Cadbury-Schweppes - spent over $850m in marketing their major sweetened beverage brands in the US in 2003, and were all among the top 100 corporate spenders on advertising that year.
According to the researchers on the new study, led by Dr Jean Wiecha of the Harvard School of Public Health, children in schools are three times more likely to purchase sugar-sweetened beverages from school vending machines than any other product. Water is the next most popular product, followed by ice cream.
But beverages such as nondiet sodas, iced teas, fruit drinks and sports drinks provide most or all of their calories from refined carbohydrates, and have little or no inherent nutritional value.
Linked in previous studies to both an increased body mass index and obesity, sugary drinks contribute more added sugars to Americans' diets than any other foods. Consumption of added sugars peaks in the adolescent and teen years at about 20 percent of daily calories, whereas experts recommend no more than 6-10 percent.
According to a study conducted in 2000, among 12 to 17 year-olds, nondiet soda provides 40 percent of all calories from added sugar, while sweetened fruit drinks contribute an additional 11-13 percent.
The nation's Dietary Guidelines recommend that Americans consume foods with little added sugars or caloric sweeteners, while the American Academy of Pediatrics emphasizes the need to restrict soft drink access to reduce related health problems, ranging from overweight to dental caries.
This month's study, which was based on a self-report survey conducted with 6th or 7th grade students, revealed that the average daily intake of sugary drinks was 1.2 servings. Boys were found to consume more of these products than girls, and blacks and Hispanics also showed higher intake levels.
"Because sugar-sweetened beverages are the largest single contributors to added sugar intake in the United States, reduction in their use has tremendous potential to curb intake of nonnutritive calories," wrote the researchers.
"For example, the roughly 15 teaspoons of sugar in a 20-oz nondiet soda exceeded the entire daily limit for added sugar intake for most individuals recommended in the USDA's 1992 Food Guide Pyramid," they added.
But although schools remain a primary target for reducing children's soda consumption, implementing vending machine restrictions can only have a limited impact. A study published in 2003 revealed that about half of children's soft drink consumption occurs at home, while 22 percent occurs in fast food restaurants.
So as well as taking measures in schools, Wiecha and her colleagues suggest the need for consumer education efforts to encourage parents and children to identify and reduce all sources of sugar-sweetened drinks, and to replace these with healthy substitutes.