Amanda Rouse, 15, might have expected some thanks when she stopped a school bus that had careered out of control. Instead, she was awarded a detention.
The teenager was sitting on the bus with 40 younger children when the driver hit her head after going round a bend.
The brave schoolgirl jumped into the seat, slammed on the brakes and brought the bus to a halt before anyone was hurt.
But teachers at Marina High School in California were not impressed, as she should have been in school at the time.
It is not known whether she had a licence to drive a bus either.
Amanda said she had asked the driver for a lift because she felt sick at school.