In time, every child will grow up. Harper Lee shows that Jem changes considerably in the course of the novel “To Kill a Mockingbird” and describes a detailed transformation from a boy to a mature man. This is reflected when Jem’s attitude to Scout had a dramatic shift, his values changed from his childhood to adulthood and Jem becomes more thoughtful than before. Without question, Jem totally changed. Firstly, as the novel progresses,Jem’s attitude to Scout is different .His changing attitude toward Scout is an important measurement of his development from innocence towards experience. At the beginning of the story, Jem plays with Scout. He treats Scout as playmate and equal. But after Scout started going to school, Jem does not want Scout to embarrass him in front of his fifth-grade friends. Later he and Dill develop a friendship from which Scout is partly excluded because she is a girl. After one altercation with Scout ,Jem hollered to Scout; “It’s time you started being a girl and acting right！“（115）.Jem realizes that Scout is a girl and she may do things like girls. Jem becomes more aware of the difference in age between himself and his sister. He wants Scout to leave him alone. Secondly, Jem changes his views towards many things such as his views to Boo Radley and other people who lived in Maycomb. After the lawsuit happened in that unstable environment, he transforms his former values. He used to do many mischievous things with Scout such as went to the Radley Place but he would conceal information to their father, Atticus. In time something changes ,when Dill escapes from his home because he has been bound in chains and left to die in the basement by his new father who disliked him. After Jem learns of that, he thinks that Dill should let his mother know where Dill is and tell Atticus that Dill is in theirs home. Scout felt very surprised by desire to ;“Then he rose and broke the remaining code of our childhood”(141).Jem’s views on things become different from what he originally thought. He has his new found perception to what happened Thirdly, Jem thought things through deeply. On the surface, he seems quicker than scout to put Scout to put the trial behind the mind, but inwardly, he has been more disturbed than Scout by the events of the trial, he was suddenly furious when Scout mentioned about the courthouse again. He leaped off the bed and shook Scout. ”Atticus said that Jem was trying hard to forget something, but what he was really doing was storing it away for a while, until enough time passed“(247). He is probably the only one in town who really believes that justice will be done and that Tom Robinson is innocent. When this does not happen, his disillusionment is so great that for a time he cannot stand even to talk about the incident. He knows that now he cannot figure it out. But long after he will be able to think about it and sort things out. So Jem becomes wiser that before. In conclusion, Jem changes from being an innocent boy to an experience and mature young man. With the development of the novel, Jem’s attitude towards Scout changes from treats her like playmate to do not play with her any more because he comes to realize she is a girl. His outlook on life and his values also changed because of the lawsuit of Tom Ronbinson.Besides, Jem is more intelligent progressively.