At least 18 people were hurt when smoke filled a school bus on Thursday.
Northwest Preparatory Academy officials said the driver noticed smoke while she was traveling on the Eastex Freeway.
The driver got off the freeway at the nearest exit and the students got off the bus, officials said.
"It was too much smoke," student Tonea Holmes said. "I couldn't breathe at all. Smoke was floating in the area. Every time she stopped, that's when smoke was coming up."
The 40 students on board were loaded onto another bus and taken to the school in the 600 block of Charles Street.
School officials later called paramedics, who found that 18 of the children had elevated levels of carbon monoxide. The students, ages 5 to 12 years old, were then taken to Memorial Hermann Northeast Hospital as a precaution. Many parents went to the hospital to be with their children.
Humble police said the smoke was caused by transmission fluid that leaked onto the engine.