A new report from the Insurance Institute for Highway Safety gave top ratings to 15 of 60 child car booster seats.
The institute crash-tested and analyzed 60 models with a dummy the size of an average 6-year-old and rated 9 as Good Bets, 6 as Best Bets; 11 were are not recommended, the report says.
Booster seats elevate children so seatbelts will fit their small frames to protect them in a crash. The institute study focused on fit, it said, because safety belts are designed for adults -- not kids.
A good booster routes the lap belt flat across a child's upper thighs and positions the shoulder belt at midshoulder. The Institute released its first booster ratings last year, evaluating 41 seats.
"Parents can't tell a good booster from a bad one just by comparing design features and price," says Anne McCartt, Institute senior vice president for research. "What really matters is if the booster you're considering correctly positions the safety belt on your 4 to 8-year-old in your vehicle. Our ratings make it easier to pick a safer booster for kids who have outgrown child restraints."
"The main thing boosters are supposed to do is provide a good belt fit," McCartt told ABC News. "So it is somewhat surprising that some boosters aren't doing that very basic job."
Booster seats are different from common car seats used for toddlers because they do not attach to the vehicle.
"We're confident we're giving consumers a solid overview of what they'll find when they shop for their children," McCartt says, adding that "parents don't need to dig deep into their pocketbooks to buy a booster with good all-around belt fit."
Best Bets and Good Bets include several affordable choices starting at about $20 and ranging up to $250 or more. Big box retailers stock most of them in stores and online, and the rest can be found at specialty baby-gear sellers.
Parents should not immediately throw out one of the "not recommended" seats, McCartt said. Statistics show that children riding in boosters are 45 percent less likely to get hurt in a crash compared to children only using seat belts, according to the report. Parents should keep using it until they decide to get a better one, because "any seat is better than none at all," according to the report.