Most children can stop using a booster seat once they are at least 4 feet 9 inches tall. This usually occurs between the ages of 8 and 12, but age alone does not determine when a child can stop using a booster seat.
To ride with a seat belt rather than a booster seat, a child must be able to sit all the way back with her knees bent at the seat. The shoulder restraints must cross between the neck and arms, and the lap restraint must rest as low as possible and touch the child's thighs. Finally, the child must be able to stay seated like that for the entire duration of the trip. Once a child can sit like that, and once the height requirements are met, the child can switch from using a booster seat.