What does Jem expect the verdict to be? Does Atticus think the same? What do you expect it to be?
Jem expects a "not guilty" verdict. Throughout the trial, he finds it obvious that Tom is innocent. When Atticus reveals that Mayella was beaten by someone who is left-handed, & Tom has no left arm, Jem whispers "We've got him." He is clearly convinced of Tom's innocence, & thinks everyone else will be as well. When Atticus finds out the children are in the courtroom, he orders them to go home, prompting this conversation:
"Aw, Atticus, let us come back," pleaded Jem. "Please let us hear the verdict, please sir."
"The jury might be out and back in a minute, we don't know--' but we could tell Atticus was relenting. “Well, you've heard it all, so you might as well hear the rest. Tell you what, you all can come back when you've eaten your supper-eat slowly, now, you won't miss anything important-and if the jury's still out, you can wait with us. But I expect it'll be over before you get back."
"You think they'll acquit him that fast?" asked Jem.
Atticus opened his mouth to answer, but shut it and left us.
Thus, Jem clearly expects Tom to be acquitted, but Atticus is not so sure. Atticus knows the disposition of the town, & he knows they don't really have a chance. For him, it's almost enough that Tom got a good lawyer who was willing to fight for him. Otherwise, there would be no question of the verdict. All of this may have gone through Atticus' mind as he opened his mouth, perhaps to tell Jem not to get his hopes up. But he doesn't speak, & chooses to let Jem realize this on his own.
The last question is subjective, but I had no illusions that Tom would be found not guilty. It is established fairly clearly that Maycomb is not progressive or compassionate enough to consider that outcome.
Jem is young and innocent and thinks that the facts presented will prove that Tom Robinson is innocent. WHat he does not realize is the world is full of racism and the court will go based on the facts, but will instead go based on what is the color of their skin. Atticus realizes that nothing can be done with these people but still gives a fair trial.