At the beginning of the book Scout tells us that, "Jem and I found our father satisfactory" (Ch. 1). This is a funny way of saying, "He was okay." She later tells us that he didn't play any sports (specifically football), didn't hunt, and didn't go out much. She also notes how old he is, almost fifty, which seems older than some of the fathers of other kids in Maycomb.
However, as the story progresses we see both Jem and Scout begin to develop real admiration for their father. Some of this begins when Atticus has to come home to shoot a rabid dog that is wandering down the middle of the street towards their house. He is a crack shot, which surprises both kids since they didn't even know he knew how to shoot a gun.
Later, as he represents Tom Robinson they recognize the difficult position he is in during the trial and they gain much respect for him as they watch his defense of Tom. Jem becomes so invested in Tom, as a result of Atticus's efforts, that he cries when Tom is convicted. This shows that Jem has begun to admire the work his father is doing and agrees with his beliefs and actions.