What is Jem's theory about why the Finches the Cunninghams the Ewells and the Robinsons are different?

Jem believes that the differences among the families stem from their place in society, specifically their social class and upbringing. He sees the Cunninghams as hardworking but poor, the Finches as respectable and well-off, the Robinsons as victims of discrimination, and the Ewells as troubled and dishonest due to their circumstances.