NEW YORK — Obesity rates have declined among New York City's public schoolchildren in kindergarten through eighth grade over the past five years, said a government study published Thursday.

The study published by the federal Centers for Disease Control and Prevention said obesity dropped from 22 to 21 percent overall between the 2006-2007 and 2010-2011 school years.

The CDC report called the 1 percent drop the biggest documented decline in childhood obesity in a large U.S. city.

City Health Commissioner Thomas Farley said the report validates public health policies developed under Mayor Michael Bloomberg's administration, aimed at combating the decades-long rise in obesity rates among children.

"That ever-rising tide of obesity is finally beginning to ebb," Farley said.

He said national obesity rates have plateaued or increased slightly, making the findings of the report that much more significant.

The study analyzed body mass index data collected by physical education teachers using standard guidelines and reported to the Department of Health. It found that while obesity decreased for children in all groups, black and Hispanic children lagged. The largest decrease — from 20 percent to 18 percent — was in children ages 5 to 6.

Farley said more needs to be done to get the rates down among low-income and black and Hispanic children.

"Unfortunately, the benefits of this were not in the children that needed it the most," he said.

The report notes policy changes from 2003 to 2009 that might have contributed to the overall drop. Those include regulations to improve nutrition, increased physical activity time, and changes to cafeteria food. Modifications to cafeteria food included switching from whole milk to 1 percent fat and skim milk in 2005.

School nurses also were trained to identify children with weight problems and to educate the community, the report said.

Dr. Achiau Ludomirsky, chief of pediatric cardiology at New York University Langone Medical Center, called the report significant.

"It looks like something is working," he said, adding that the combination of public health policies, involvement of nurses and education were likely contributing factors in the decline. "I think it's pretty encouraging, and we need to put more resources into that."