My daughter still uses a child safety seat (a.k.a. car seat), but with her booster seat days ahead of her, you can understand my interest in a recent study that looked at which booster seats successfully improved the fit of the lap and shoulder belts—and which failed.

The study, performed by the Insurance Institute for Highway Safety (IIHS) and the University of Michigan Transportation Research Institute, examined the effectiveness of booster seats, which elevate a child so that safety belts are properly positioned to protect and restrain the child in the event of a crash.

Researchers examined 41 booster seats designed to position a child at a suitable height so that the seat belts fit properly and protects the child in the event of a crash. Since booster seats are not built to restrain a child during a crash, researchers focused only on the fit of the lap and shoulder belts when a booster seat was used and not crash protection.

Because seat belts are designed to fit adults, they don’t properly fit most kids until they reach a height of 4 feet and 9 inches or more. Tragically, about 350 kids ages four to seven die each year in the United States and an additional 50,000 are injured in accidents involving motor vehicles. Half of the fatalities were found to be unrestrained.

According to IIHS president Adrian Lund, a good booster seat will route the safety belt to insure that the lap and shoulder belts are well-positioned across the child’s bony parts and not soft areas such as the abdomen, which is more vulnerable to injury during a crash. When a child is placed in a proper booster seat, the shoulder belt will be at mid-shoulder with the webbing away from the neck. This reduces rubbing and chafing and the likelihood that kids will just get frustrated and put the belt behind their back or under their arm.

Researchers examined backless and highback boosters in a wide range of vehicles. Emphasis was placed on lap belt fit. And based on the results, I’m going to be shopping for a new booster seat when my daughter reaches 4 feet 9 inches. Unfortunately, I purchased one of the child safety seats marketed as “the only/last seat you’ll need to buy,” the appeal being the projected savings that come with a seat that converts from child safety to booster.

However, my “combination” seat is among those not recommended by the IIHS due to poor seat belt fit. The main problem with the models that tested poorly, say researchers, is that they leave the lap belt partially or fully resting on the child’s abdomen. But that’s not all.

Researchers used a Hybrid III dummy as a six-year-old child (the average age of a child using a booster seat.) While backless boosters generally provided better lap belt fit, only one—the Graco Turbo Booster with belt positioning clips, provided both proper lap and shoulder belt fit.

Highback booster seats generally scored better when it came to positioning the shoulder belt due to built-in guides. But 12 of the 25 highback boosters tested failed to properly position the lap belt.

So how did the boosters rate? Results follow:

Not recommended by the IIHS:

• Safety Angel Ride Ryte backless
• Cosco/Dorel (Eddie Bauer)
• Summit Graco CarGo Zephyr
• Evenflo Big Kid Confidence
• Cosco/Dorel Traveler
• Compass B505
• Compass B510
• Evenflo Generations
• Dorel/Safety 1st (Eddie Bauer) Prospect
• Cosco Highback Booster
• Cosco/Dorel Alpha Omega
• Evenflo Chase Comfort Touch
• Safety 1st/Dorel Intera

Best Bets as determined by the IIHS:

• Graco TurboBooster backless with clip
• Fisher-Price Safe Voyage backless with clip
• Combi Kobuk backless with clip
• Fisher-Price Safe Voyage
• Britax Parkway
• LaRoche Bros. Teddy Bear
• Safeguard Go backless with clip
• Volvo booster cushion
• Recaro Young Style
• Britax Monarch

Good bets as determined by the IIHS:

• Graco TurboBooster
• Safety Angel Ride Ryte
• Recaro Young Sport
• Combi Kobuk
• Safety 1st/Dorel Apex 65

I can only imagine what you’re thinking right now if you’re looking at this list and your child’s booster seat is not listed as a good bet, or worse, is listed as not recommended. But before you run out and buy a new booster seat, put your child in their booster seat in your car and see how the belts fit. Unlike Hybrid III dummies, kids come in different sizes, moreover they fidget and slouch. Some booster seats may be better suited to a particular child in a particular vehicle depending on the size and shape of the child and how the belts are installed.

If you do happen to find yourself in the market for a new booster seat, it may help to know that it’s not likely to break the bank. The Highback Graco Turbo Booster converts to a backless model and sells for about $50. Or you can buy the backless version for about $20. Whatever you decide, the experts agree that between the ages of four and eight, any booster seat is better than none at all.