You asked why. I stated a possible theory.Student A is the product of two well-educated parents who placed an emphasis on education their entire lives. This student went to the finest private schools, had the best tutors and was groomed and shipped-off to school with a fistfull of cash and zero debt.
Student B is the product of two uneducated parents, one of which is an alcoholic. Neither value education at all. This student went to PS32 and majored in fogging. This student barely made it into school by hocking his entire life and will work his way through college with a 40 hour/week job.
And Student A's better grades are pure skill?
I wasn't making a comment on the possibility of the theory.