The National Highway Traffic Safety Administration does not require seatbelts for larger school buses, believing the bus design – with high back, padded seats – offers enough good protection. A few years ago, the requirement for the seat height was increased from 20 to 24 inches to improve "compartmentalization."
NHTSA did, in 2008, "encourage" districts to put in seatbelts if they had the financial wherewithal and felt it was a good safety move.
The district's buses have been recently inspected in anticipation of the start of the school year, according to Missouri State Highway Patrol. One bus failed the inspection, but with a minor problem that was fixed on the spot.
Thirty-five of the children on the buses were being transferred to Cardinal Glennon Children's Medical Center in St. Louis for treatment. None of those children are believed to have serious injuries.
"They are all listed as green patients, which means they have light injuries and most of them are up and walking around," said Mary Aita, public relations officer for the hospital.
One child initially being transported to Glennon was rerouted to St. Louis Children's Hospital. Aita speculated that it may be because the individual was more seriously injured.
Four other students are being transported to St. John's Mercy Hospital. Their condition is unknown.
The crash occured on Interstate 44 near Gray Summit, which is about 40 miles southeast of St. Louis.
Rescue ladders can be seen leaning into the windows of the buses.
Traffic was backed up on the highway for 10 miles after the crash.
The Federal Motor Carrier Safety Administration which oversees commercial trucking has representatives either heading to, or already on scene of the crash.
ABC News' Susan Caraher and Lisa Stark and The Associated Press contributed to this report.