Is there any other evidence relating to Jem's maturation in To Kill a Mockingbird besides Jem urging Scout to stop antagonizing Aunt Alexandria?
Like sister Scout, Jem also matures during the time frame that encompasses To Kill a Mockingbird. One of his first learning experiences came when the children's secret knothole was cemented by Boo's brother. Mr. Radley told Jem that he enclosed the knothole because the tree was dying; Atticus explained that the tree was fine, and Jem realized for himself that Radley had lied. He had closed off the hiding place so Boo could no longer communicate with his young neighbors.
Jem grew up a bit more following the death of Mrs. Dubose, and took another big leap when he recognized the injustice of the jury's verdict against Tom Robinson, declaring that "they oughta do away with juries." He became upset later when Scout mentioned Miss Gates' conversation at the courthouse, telling Scout angrily that "I never wanta hear about that courthouse again, ever, ever, you hear me?" But perhaps the most important sign of Jem's growing maturity came when he first entered the seventh grade: Now a high schooler, he went out for the football team (but he was so small that he was only used as a water boy).