ARLINGTON, VA — Booster seats are meant to do one thing — elevate children so that safety belts designed for adults are in the right position to restrain kids during a crash. Thirteen of the 41 belt-positioning booster seats the Insurance Institute for Highway Safety evaluated with the University of Michigan Transportation Research Institute did such a poor job of improving the fit of lap and shoulder belts for children that the Institute doesn't recommend them at all. Ten models are best bets and 5 are good bets. These evaluations are the first to tell consumers how well boosters sold by US retailers improve belt fit for children in cars, minivans, and SUVs. The Institute plans to continue these assessments.