Booster seats are the best way to keep your child safe in the car after he or she outgrows a harnessed child seat but is too small to correctly fit a vehicle's seat belt. The use of any booster seat will improve your child's safety, and likely his comfort as well. Chances are, however, that a high-back booster seat will be better on both fronts than a backless booster. (See our latest booster car seat Ratings.)
A booster seat's most important job is to properly position a vehicle seat belt across a child's chest, shoulder, and hips. Data has shown that boosters reduce the risk of injury for children aged 4 to 8 years by 45 percent versus children of a similar age that are restrained using the vehicle belts alone. (See our car seat timeline and buying advice to figure out which seat is best for your child, no matter the age.)
Many backless boosters do a decent job of positioning the lap belt on a child's hips. But in vehicles where the upper belt anchors don't fall exactly in line with the child's shoulder, backless boosters are less likely to provide a good fit. High-back boosters have upper back guides that, in most cases, position the shoulder belt properly and keep it in place. This is especially important when a youngster moves around a lot, and in vehicles where the shoulder belt anchors are positioned too close or far from the child's shoulder. (See our video on how to install and use both harnessed and belt-positioning booster seats.)
Some backless boosters do include a clip that helps position the shoulder belt. In our fit-to-child evaluations, we find that these clips do a decent job of positioning the shoulder belt if everything is kept still, but when we move our child dummy to simulate a child moving, the belts easily slip out of place on the shoulder. The flexible strap attached to the clip simply can't hold it in place.
A high-back booster also provides head support that backless boosters do not. This is especially important if your vehicle doesn't have headrests in the rear seat, or if the headrests are not tall enough to protect your child's head when the booster is in place. The instructions included with most backless boosters prohibit their use in vehicle seating positions where the child's ears or the mid-point of the child's head would be above the vehicle seat back or head restraint. Most high-back boosters provide that protection even for vehicles seats that lack a head restraint.
High-back boosters also provide head protection from the side, as well as the convenience of a spot for a sleeping child to rest their head. Side bolsters, or 'wings,' as they are sometimes called, help to contain the head during an impact, and often contain foam designed to absorb energy in a crash. One study found that children in high-back boosters were 70 percent less likely to be injured in a side-impact crash than children in seat belts alone. The same study found that in a side impact crash, the risk of injury to children in backless boosters was not significantly different than if they were wearing seat belts alone.
There are high-back boosters that allow you to remove the back so they can be used in backless mode. Before you go this route, consider this: We found that vehicle safety belts fit better on dedicated backless boosters than they did on high-back models with removable backs when used in backless mode. This was true for fit of both the shoulder belt and lap belt.
While high-backs are the safest choice, backless boosters are still much safer than no booster at all, and we can see some legitimate reasons parents might choose a no-back model. For one thing, backless boosters are generally less expensive, some costing as little as $14. And no doubt about it--backless models are easier to transport. This can be important if you have an active, school-aged kid who is still too small to fit vehicle belts and you'll be switching cars while carting him to and from school and activities.
All boosters have a minimum weight requirement for children to use them. Be aware that many backless boosters have higher weight minimums than high-back models. Be sure to check the weight requirements before you use them. But as long as your child can properly fit in a safety seat that uses an internal harness (such as a harnessed booster seat), that is the safer place for him or her to ride.
When to move on: The 5-step test
When you can answer 'yes' to all of the following questions, your child is ready to safely sit on a vehicle seat without a booster:
- Does your child sit all the way back against the vehicle seat?
- Do your child's knees bend comfortably at the edge of the vehicle seat?
- Does the vehicle belt cross your child's shoulder evenly between the neck and arm?
- Is the lap belt as low on the abdomen as possible, near the top of the thighs?
- Can your child stay comfortably seated like this for the whole trip?
- Does the belt stay in place when the child moves?
If the answer to any of these questions is no, then a booster is still the safest, and more than likely the most comfortable, way for your child to travel.
And see our Ratings of infant car seats, convertible car seats, all-in-one car seats, and harnessed booster seats for more information.