Here is news story:
CBS News

The full report:
Booster Report

A statement from SafeKids:

The Insurance Institute for Highway Safety issued a report today questioning how much booster seats improve seat belt fit. We know that booster seats save lives. We also know that kids come in all shapes and sizes and not every seat will fit every kid. Instead of stating that clearly, the message this report sends is that 13 of the 41 boosters IIHS tested were rated as “not recommended.” We should use this report to remind parents of the importance of proper fit when it comes to boosters and seat belts. We expect coalitions to get calls from their local media looking for advice. Please use the information and tips below as a guide. This is also posted on the Safe Kids USA website.

Booster Seats are Not-One-Size-Fits-All
Parents Must Find the Right Fit for Their Child
Booster seats are a proven way to help keep kids safer in vehicles. In fact, for children 4 to 7 years old, booster seats reduce injury risk by 59 percent compared to seat belts alone, according to researchers at the Children's Hospital of Philadelphia.

But a report released today by the Insurance Institute for Highway Safety has questioned if certain booster seats provide children with a better fit than others. Kids come in all shapes and sizes, and not all boosters will fit all children the same way. There are no “good” seats and “bad” seats as the IIHS list might suggest—all meet the government standard in crash tests. But booster seats are not designed to be one-size-fits-all. The different variations in boosters allow parents to find the right fit for each child.

It’s All About Fit
Parents and caregivers should not panic and they should continue to use booster seats for their children on every ride. However, there are a few simple steps parents can take to make sure a child’s booster fits the correct way.

Safety belts are designed for adults and many children are too small to get a proper fit without using a booster seat. Most children who have outgrown their toddler seats but are still under 4 feet 9 inches tall and less than 80 pounds will be safest using a booster seat.

Take this easy fit test with your child to determine if a booster seat fits your child:

Place your child on the booster seat and fasten the lap and shoulder seat belts around the child.
Use the seat belt guides on the booster seat for the lap and shoulder belts.
Check to be sure the lap belt rests on the top of the thighs or low on the hips.
Check to be sure the shoulder belt is positioned on the bony shoulder- not the neck or face. Never place the shoulder belt under the arm or behind the back.
If the shoulder belt and lap belt are on the child as stated above, the booster seat will work as designed to protect your child in a crash. If not, try another brand until you find the one that fits your child. Fortunately, there are lots of choices.

If you’re confused or would like a certified child passenger safety technician to evaluate your child, go to SafeKids.org to contact your local Safe Kids coalition by clicking on “find coalitions and events near you.”

SeatCheck.org