A new study looked at 83 booster seats for children and evaluated their fit in a vehicle using an adult sized seat belt.  However, 41 of those booster seats fell into the “check fit” category.

This means almost half of the seats tested might not provide adequate seat-belt fit for all children in all vehicles.  Parents with booster seats should check that the booster makes the lap belt lie flat across the child’s upper thighs.

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Most of the reason the different car seats don't fit with every vehicle is because car companies design their cars different as well as the placement of their seat belts.  The rankings are available online.

31 seats did fall into the "best fit" category.  This means those 31 seats, when properly positioned in all vehicles, they fit correctly with the seat belt.  Experts say when parents are shopping for a booster or car seat, they should first take a look at their particular vehicle(s) and notice how the seat belt is positioned in and of itself.

The report was done by the Insurance Institute for Highway Safety.