The Ewells are meant as a foil to the exclusion of the african american citizens of Maycomb. The Ewells are so repugnant that society deems their recovery as a worthless enterprise. The question then is will the word of this family be held in higher esteem than other citizens that excluded for reasons that are not based on conduct.
The rules are somewhat bent for the Ewell family. They are very poor, and the only government checks that Bob Ewell gets he spends on alcohol. So, he is allowed (even though it is illegal) to hunt and trap out of season. Atticus tells Scout that all of the farmers and land owners of Maycomb county agree that those kids need some sort of food, so anything he can hit, they allow him to in order to feed those kids.
Another thing that is different about the Ewells is that they only have to go to school for one day. They are made to go that first day, but after that, the Tardy Lady doesn't bother them anymore. They are such a poor family, and according to Atticus, "they live like animals." Most of the families don't want them in school with their kids, so they just let them get away with skipping school.
In Chapter 3, Scout comes home from a rough first day of school and tells Atticus that she does not want to return. Scout says to her father that Burris Ewell does not have to attend and only has to show up on the first day. Atticus then explains to Scout that Burris Ewell is an exception and mentions how sometimes it is better to bend the law in "special cases." Atticus elaborates by telling Scout how the Ewells are the most despicable people in Maycomb and says that they live like animals. Atticus also explains to Scout how the citizens of Maycomb allow the Ewell family certain privileges like hunting out of season because their father, Bob Ewell, is an alcoholic who struggles to feed his children. Scout learns that Bob Ewell squanders his relief checks on green whiskey while his children starve. The citizens of Maycomb understand that if Bob weren't allowed to hunt and trap out of season, his children would not eat. Atticus also tells Scout that the Ewells will never change their ways which is why in certain cases it is necessary to bend the law.