Bus Radio, a Massachusetts-based company, says 100,000 riders on 800 buses will hear music and commercials. The company says the broadcasts will entertain children and curb rowdiness.

"We want a safer ride. We don't approve of what's being played" now, says company CEO Michael Yanoff. He says more than half of school buses nationwide are equipped with FM radio that airs adult content, including commercials for beer and R-rated movies.

Bus Radio will broadcast age-appropriate ads and music by pop singers such as Kelly Clarkson, Yanoff says. Content varies by riders' ages. He would not name participating schools or advertisers but says products will cover entertainment, apparel, electronics, education and health.

Opponents of advertising to children object to the programming.

"This is a marketing ploy" aimed at "sedating" kids, says Susan Linn, a psychologist with the Campaign for a Commercial-Free Childhood, a Boston-based group.

"Advertisers love marketing in school, because children are a captive audience. This extends that to the school bus," says Linn. "Kids are already bombarded with advertising." She says ads are linked to childhood obesity, underage drinking, violence and other problems.

Linn says more ads are not the solution to inappropriate radio or misbehavior on buses. "We have to find another way to deal with that."

Reports of aggressive and violent behavior on school buses are increasing, according to National School Safety and Security Services, a consulting firm.

Playing the radio can be a reward for good rider behavior but won't prevent serious incidents, says Kenneth Trump, the firm's president. "It's not a cure-all."

Radio on the bus helps keep students "focused," says Linda Farbry, director of transportation for Fairfax County Public Schools in Virginia, the nation's 13th-largest school system. She says most of the district's buses play radio from an approved list of stations, and because the ads aren't directed at students, kids easily ignore them. Farbry opposes Bus Radio because she says it would be harder for kids to tune out ads geared to their interests.

Bus Radio's one-hour broadcasts contain six minutes of public service ads and eight minutes of commercials. Yanoff expects the service to expand to 1 million students next year. Yanoff says schools will be paid based on number of students, length of contract and frequency of broadcasts. He wouldn't be more specific.

The schools are in 11 states: California, Georgia, Indiana, Massachusetts, Michigan, New Jersey, Ohio, Oklahoma, Pennsylvania, Tennessee and Washington.

Democratic Sen. Byron Dorgan of North Dakota has added an amendment to a pending bill that would require the Federal Communications Commission to study proposals to advertise on school buses.