CHICAGO (AP) -- A new study suggests that junk food remains plentiful at the nation's elementary schools despite widespread efforts to fight childhood obesity.

Between 2006 and 2010, nearly half of public and private schools that were surveyed sold sweet or salty snack foods outside of lunch and breakfast.

The study found little change over the four years. It was released Monday in Archives of Pediatrics & Adolescent Medicine.

It focused on snacks sold in vending machines and other places during times other than school meals. Until recently these foods weren't subject to government nutrition standards.

But a law enacted in December 2010 gives the U.S. Agriculture Department authority to set those standards.