Why is it that one child has severe asthma but a sibling, who grows up in the same household, is fine? Why is it that one town seems to have more children with autism than other areas? Why do some children get sick more than others?

The federal National Children's Study hopes to answer these questions and many more over the next few decades. Last week, the study took a major step forward by naming six centers at major medical institutions around the country with a goal of recruiting patients beginning in 2007. The centers' study teams will work within the communities to recruit pregnant women and those who might become pregnant.

Researchers will follow the development of the children through pregnancy and, study organizers hope, into adulthood. They're aiming to follow about 100,000 children, noting everything from the quality of air the children breathe to the amount of time they spend in front of a computer.

"There's never been a study this large or this ambitious in children," says Alan Fleishman, chair of the study's advisory committee. "It's a very broad look at how the environment impacts on growth and development."

U.S. News wrote an extensive story about the National Children's Study when it was announced earlier this year.