Some kids just don't listen.
Parenting IS important, no doubt, but there are always those families that have three kids, and two of them are exemplary students, well behaved, and one is a major jerk, screws off in school, and is the black sheep and he/she was raised by the same two parents as the other two kids.
Some kids are harder to manage than others. I figure the Lord gives them the personality to do the work He has planned for them. You may have to invest more time and discipline in some but it pays off. That "black sheep" rebellious time is a learning curve IMO.