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Four years older than his sister Scout, Jeremy "Jem" Finch seems to have a deeper understanding of the events during the three years of the novel, for his emotional reactions to them are stronger. Scout spends much of her time with her older brother Jem and is constantly trying to prove herself his equal.
They are different based on the levels of maturity. Jem is more mature than Scout, showing a lot of growth in the process of the book, reaching adolescence and had experienced hardships and turbulent times in his entire life that gave him spiritual growth, while Scout has a bit of "child-like" mind.