In "To Kill a Mockingbird" by Harper Lee, Jem certainly does not having something symbolize him in the manner that Lee employs the mockingbird to symbolize Tom Robinson and Boo Radley. However, if the reader must assign a symbol for him, perhaps a storm could represent Jem, whose mercurial nature clearly manifests itself during his puberty.
Jem is much more emotionally responsive to situations than Scout. For instance, he is often exasperated with Scout and asks her in brotherly fashion to stay away from him and not talk to him at school. Always eager to please his father, he also wishes to defend him and overreacts when men come into the front yard one evening before the trial. When the verdict for Tom Robinson is given, Jem is adversely affected, both emotionally and rationally; he cannot understand how a guilty charge can be given. This disillusionment brings dark clouds of melancholy upon him, and Jem is greatly disappointed in people. Nevertheless, the clouds of disillusionment part and Jem becomes a wisened and more mature young man.
In To Kill a Mockingbird,” Jem symbolizes “growing up," or maturity. From a young boy still playing games and being more concerned about what new adventure he’ll get into, he matures into a young adult dealing with the problems and conflicts of a man.
Everything he encounters is a learning experience for him: Tom Robinson’s trial and conviction, finding out about who Boo Radley really is, and dealing with the attack and death of Bob Ewell all lead to Jem’s induction into the real world of adulthood. Sometimes it wasn’t a pleasant journey, but it was one that taught him many lessons and prepared him for his future.