Atticus, as a single father, has a difficult job, especially since there are so many undesirable influences on Jem and Scout in the community. However, he excels at parenting and, with the help of Calpurnia, is raising wise and honorable children.
At first, Atticus seems distant, allowing his children free-reign for much of the time. Calpurnia seems to bear the brunt of being the disciplinarian. She is responsible for the daily tasks, while Atticus seems just to show up to deal with the larger issues.
Yet it is in these larger issues that Atticus shines forth. Atticus is developing their character and their moral worldview. Rather than focusing on surface issues, Atticus delves to the foundation, the moral basis for decisions to be made. Rather than dealing with the "irritation" factor of the children's bothering Boo Radley, he teaches them to see the dignity of Boo, rather than his strangeness that makes him such a butt of all the jokes. He teaches them the inherent value of all people--Boo, Tom Robinson, etc. He develops empathy, so that Jem and Scout are able to draw themselves out of their self-centeredness and view people in light of the battles they have fought, won, and at times lost.
Atticus treats each child as an individual, meeting them on their own terms. He treats Jen differently from Scout, not because he is a boy, but because he is Jem and is different from Scout. He has the ability to see deep into his children's character, tap into their strengths to allow them to shine forth, as well as dealing with their weaknesses.
Atticus is an excellent parent because he is realizes he is not raising children, he is raising potential adults. The joys of childhood are a preparation for being a responsible, honorable grown-up, and it is their later lives, not the passing whims of childhood, that Atticus is concerned with developing. He views childhood as a time for learning, and play is for learning's sake, not just for play's sake. Everything is a lesson. Therefore, it can be said that it is not so much that Atticus is an excellent father, but that he is an excellent teacher. But perhaps that's what parenting is all about after all.