I think the parents should set up a reward system for their kids to get good grades. But what I learned in a Psychology class many moons ago that if it is a money reward it should not be too high. For example it was better to reward a child a dollar than ten dollars because if you set the reward higher then the child would consider it to be work and it would be better to set the reward lower so the child would think learning as fun.
Schools do offer reward in the form of scholarships, but they only are offered to a select few. But the schools can offer other types of rewards, especially if a child is struggling in a class.