Dozens of other students from the John F. Hodge High School in St. James were taken to hospitals for treatment after the crash, which happened on a highway near Gray Summit, about 40 miles west of St. Louis. Most of the injuries were minor, and only two students remained hospitalized Thursday evening.
The students were traveling to a Six Flags amusement park about 10 miles from the crash site.
According to the State Highway Patrol, a pickup truck driven by 19-year-old Daniel Schatz, a former reserve quarterback for the University of Missouri football team and the son of Republican state House candidate Dave Schatz, slammed into the back of a semi cab that had slowed approaching a construction zone.
The forward-most of the two buses carrying the St. James students slammed into the back of Schatz's truck, then landed on top of it after it was rammed from behind by the other bus, said Highway Patrol Cpl. Jeff Wilson.
Jessica Brinker, a 15-year-old student who was sitting in the back of the first bus, was killed, the Patrol said.
Kolby Griffith, 17, said he was chatting with friends on the second bus when it crashed, and that everything happened so quickly it was a blur.
"It was all very, very quick," Griffith said. "I was trying to get away, trying to get everyone away from the bus because I could smell gas."
Griffith, who was evaluated and released at SSM Cardinal Glennon Children's Medical Center in St. Louis, was among about three dozen students who were called into a room at the hospital and told about Brinker's death.
"There's a lot of pain," he said, choking back tears.
A huge crowd gathered Thursday evening for a hastily called prayer vigil at a middle school in St. James, a town of 3,700 residents 86 miles southwest of St. Louis that is known for its wineries and outdoor splendor.
"Anytime you have something like this, it is a big tragedy for a community," the town's mayor, Dennis Wilson, said earlier. He described the community as "one of those towns where you know just about everyone in town and know their kids," including the nearly 600 children who attend Hodge high school.
Joy Tucker, the superintendent of the St. James school system, said it was a "horrible, horrible day" for the community.
"We'll never get over this," she said.
Schatz was an all-state high school football player. He made the Missouri squad as a walk-on in 2009 but didn't get into a game, his father said. Daniel Schatz left Missouri and hoped to play alongside his older brother at Westminster College this fall.
Daniel was driving to Schatz Underground Inc., a family owned contracting business in Villa Ridge, when the accident occurred, said his father. Dave Schatz won the Republican primary for a Missouri House seat on Tuesday.
He described his son as "a great kid."
Brinker's Facebook page included a message that read, "She was the most funniest girl to be around! always rockin the knee high sock .... we love you Jessica R.I.P."
The students injured in the wreck - nearly 50 of them - had mostly bumps and bruises and were expected to be fine, Wilson said. Thirty-six people were originally taken to Cardinal Glennon and by late evening, all but one were released. Of six victims sent to St. John's Mercy Medical Center, five were released and one was transferred to St. Louis Children's Hospital. St. Louis Children's spokeswoman Jackie Ferman said that 16-year-old St. James girl was in stable condition.
Four other victims were taken with minor injuries to St. Clare Health Center in Fenton, Mo., a spokeswoman said.
Wilson said the driver of the first bus moved into the passing lane to give a distressed vehicle in the shoulder more room. She was checking her rearview mirror while returning to the right-hand lane when she noticed the first impact but could not stop in time, hitting the pickup. The second bus then rear-ended the first, vaulting the first bus onto the top of the pickup, which was crushed.
The buses were segregated by gender, with girls in the first and boys on the other, Wilson said.
The pickup was barely recognizable in the tangled wreckage. Crews used a crane to lift the buses off of the crushed wreckage to clear the freeway, which was closed going eastbound for hours, backing up traffic for miles.
Wilson said it was too soon to say if any of the drivers would face charges.
A spokeswoman for the National Transportation Safety Board said a team of 14 investigators will look into the accident and try to determine if there's a broader safety issue.
Associated Press writers Jim Suhr and Christopher Leonard in St. Louis, Chris Blank in Jefferson City, and Heather Hollingsworth and Bill Draper in Kansas City contributed to this report.