Miami-Dade police said the shooting occurred on a private bus transporting students to several charter schools, WFOR-TV, Miami, reported.
Police spokesman Alvaro Zabaleta said the 13-year old girl was shot in the neck. The girl's name hasn't been released.
Zabaleta said a male on the bus was in custody and being questioning, WFOR reported. Police said they recovered the gun used in the shooting.
Police didn't release any information about what may have led to the shooting.
The driver and eight other children on the bus were uninjured, WFOR said.
"We are dealing with small children so the questioning process is going to be a lot different," Zabaleto said. "The children, they are already shaken up over what they had to witness and on top of that you have to question them. This is going to be a very slow and tedious process."