The crash happened at about 6.13am local time and involved three vehicles, according to the Polk County sheriff's office. The bus was carrying 39 people: 37 high school students, the bus driver and the driver's daughter.
The sheriff's office said the bus was travelling in its lane when a white Chevrolet Malibu going in the opposite direction crossed the roadway's centre line for unknown reasons and struck the bus's tandem rear wheels. The bus lost traction, had a tyre ripped off, crossed into oncoming traffic and hit a silver Jeep head-on.
The high school student killed was a girl in 10th grade at Winter Haven High School. The other person killed was an occupant of one of the two other vehicles involved. Police said about 26 students were taken to hospital.
Polk County Sheriff Grady Judd said: "It was a horrible crash. It was a terrible, tragic morning. We had a beautiful 10th grade girl lose her life."
The Polk County public school district said in a statement: "This is devastating news for WHHS and our community. We are praying for the victims and their families."
National Safety Council data cited by authorities showed 110 deaths related to school bus crashes in 2024, a 14% decrease from 128 in 2023. Over the nine years from 2015, about 71% of school bus-related crash deaths involved occupants of other vehicles, while bus passengers accounted for 6%. The council said riding a school bus was statistically safer for children than riding in a car or walking to school.