Tricia De Marzo, 48, sat behind the driver on the outing from Sacred Heart infants school near Halifax to a Lancashire theme park. Staff distracted the 30 six-year-olds while she steered the 52-seater to safety and stopped on the hard shoulder.
Mrs De Marzo said: "The children were blissfully unaware of the potential danger. They thought the driver just had a headache and that was why I took the wheel."
Luckily, the driver regained consciousness in time to tell Mrs De Marzo, who usually drives an automatic, how to use the gears.
"It wasn't until I stopped the coach I realised what had happened and thought 'what if?' I think we were kissed by angels."