Legislation passed in 2007 goes into effect this month, requiring public schools outside of New York City to collect and report a summary of students' weights and body mass indexes as part of an effort to combat childhood obesity.

"Whatever you can measure, you can improve," said Dr. Richard Daines, the state health commissioner. "By requiring the measurement of body mass index, I think we'll see some improvement."

Doctors will now be required to test students when they come in for a student health certificate - which is mandatory for attendance at New York schools. The information will be reported to schools, creating a set of data that will allow health officials to evaluate obesity levels based on geography.

"We'll have a much better sense of the distribution of the problem (and) if there are areas that have more of a problem," Daines said.

The information will be confidential and collected at school entry and in second, fourth, seventh and 10th grades.

The data will be passed on to the state Department of Health unless parents ask to have the information excluded.

A 2004 health survey of New York third-graders found that 21 percent were obese.

The body mass index reporting requirement was pilot tested during the last school year with voluntary participation by 97 schools.

As of December 2007, 12 other states had some version of student BMI reporting: Arkansas, Texas, California, Delaware, Florida, Illinois, Iowa, Missouri, Pennsylvania, South Carolina, Tennessee, and West Virginia.

Some New York City schools have been independently collecting similar data for the past two years through a program designed to promote a "culture of fitness," said Maibe Gonzalez Fuentes, a spokeswoman for the New York City Department of Education. Now about 1,000 schools participate in the program, which collects BMI information and provides students and parents with information about their health.

Click here for a list of schools participating in the program.