When Atticus was sitting outside the jail where Tom Robinson was being held, he was approached by men from the county, including Mr.Cunningham. The men wanted to hurt Tom, and they were willing to hurt Atticus for protecting Tom...
Jem saw these events unfold from nearby, and he leaped to defend his father. When his father sent him home, Jem refused, risking his safety to defend his father. "'Go home, Jem.' He said...Jem shook his head...'I'll send him home,' a burly man said..."
On a day in summer, Jem and Scout accompanied Calpurnia to her all black church to participate in a service. Already, It is inspiring that Jem would go to an all black church, because he is a white boy living in the South.
Towards the end of the service, Reverend Sykes asks everyone to donate some money to help Tom Robinson's wife. Jem gets up and donates his own money to the cause: "...the congregation came forward and dropped nickels and dimes...Jem and I followed suit."
Throughout the whole trial, Jem was very supportive of Tom. He very strongly wanted Tom to be acquitted of the crime. He knew that Robinson was only being accused because he was black, and Jem saw the prejudice behind that.
As a punishment, Jem was sent to visit her and read to her everyday. This shows kindness and compassion, because he could have just not shown up and left her alone.