Maynard and Luke may act all easygoing, but the Quinn family followed a strict tradition. Even Maynard Quinn would act virtuously in front of the elders of the clan. In other words, they treated education with the highest regard.
Luke may not look like it, but even when he didn't take school seriously, he had good grades. Having good grades in the academy they used to attend was akin to being a top student in a regular school.
Grades were simply one of the many things Luke and Asher had to abide by. It was also their reputation, as the Quinns were very concerned with their reputation. The only reason Luke got away with his rebellious attitude at the Academy was that most of his classmates were terrified of him. Backed up with good grades, the elders didn't think about what sort of things Luke was doing in school.
