Jem, Dill, and Scout go out for a walk in Chapter 6. It is on this walk that the four reasons come up. Jem keeps suggesting to Scout that she should return home. Finally when Scout convinces him to tell her what they are doing, she wants to know why they waited until that evening.

Two of the reasons have to do with the darkness. First, the dark would protect them from being seen. Second, if it was light outside, it would be more difficult to see inside since the house would be dark. Another reason is that Atticus would not catch them due to his usual practice of reading at that time. Finally, a fourth reason is that it was the end of summer, so if they died by Boo Radley's hand, they would not miss any vacation.

This causes Scout to argue but Jem eventually convinces her to come by saying, "...you’re gettin’ more like a girl every day!”

In Chapter 6, Dill and Jem say they are casually going for a walk. Scout knows that they are up to something and questions what the two have planned. Jem tells Scout to go home, and tells her that they are simply going to peep into a window with a loose shutter at the Radley’s house in an attempt to look at Boo Radley. When Scout questions them as to why they chose to peek into the Radley’s window on this particular night, Jem lists four reasons: nobody could see them at night; Atticus would be preoccupied reading and wouldn’t hear them; if Boo Radley killed them they’d miss school instead of vacation; and it was easier to see inside the house when it was dark out as opposed to the daytime. (6.69)

What reason do Jem and Dill give for trying to peek into the Radley window on that particular night in To Kill a Mockingbird?

Jem and Dill peek in the Radley window to get a look at Boo Radley.

Boo Radley is the neighborhood monster.  All of the children are afraid of him, and even the adults spread rumors about him.  He has stayed in his house since he was a teenager, and he never comes out.  Naturally he becomes a boogeyman for the neighborhood.

Inside the house lived a malevolent phantom. People said he existed, but Jem and I had never seen him. People said he went out at night when the moon was down, and peeped in windows. (Ch. 1)

When Dill joins Scout and Jem in Maycomb, he is fascinated by Boo Radley.  The children’s new game becomes to try to get Boo Radley to come out. Although they make up all kinds of stories about him and reenact his history in the yard, the children are really just curious.  Atticus tells them to stay away from Boo Radley.

Dill says that they are going to leave a note for Boo Radley offering him ice cream.  He thinks that if he comes out to sit a spell he’ll feel better.  Scout does not like the whole plan.  She wants nothing to do with Boo Radley.  They explain...