Understand, "terrible grades" are unlikely to get the kid into any sort of college. Even community colleges have their standards, as low as they might be.
So it might be more likely that the parents would be paying for technical school like electrician, plumber, HVAC, chef, etc. I list these as these blue collar jobs have the potential for earning big bucks comparable to what a college grad might earn. Aviation mechanics, for example, can earn over $75,000 per annum in the Oakland CA area.