Dr. William Bommer of UC Davis says the data show obesity levels-off once a child enters school in California.
And he attributes that at least in part to school standards for nutrition and exercise.
BOMMER: "For the first time we see a turning point that instead of increasing each year, we've been able to at least stop the increase in obesity."
Bommer looked at data for over 6 million school children from 2003 to 2008.
He says more progress in the fight against obesity should focus on pre-schoolers.
BOMMER: "There is front loading of this. That is, the kids before they get into our school program are become more obese each year."