What do you think Ray Bradbury wanted his readers to think about when they finished reading his story "All Summer in A Day"?

Bradbury likely hopes that people will take bullying seriously.

This is a story about a group of children on Venus who behave in much the same way some children do on Earth.  They target a girl different than themselves, and make fun of her.  Margot has been to Earth and remembers the sun, and for this reason the other children do not like her.

Margot keeps herself apart from the other children.  The way they treat her is a combination of the fact that she is different and the fact that she holds herself apart from them.

Margot stood apart from them, from these children who could ever remember a time when there wasn’t rain and rain and rain. They were all nine years old, and if there had been a day, seven years ago, when the sun came out for an hour and showed its face to the stunned world, they could not recall.

The other children resent Margot for remembering the sun.  They have been on Venus all of their lives, and the last time the sun came out they were toddlers.  For this reason, they bully Margot.  They get irritated when she claims to remember the sun.

When the other children bully Margot, the teacher barely intervenes.

That was Margot’s poem, read in a quiet voice in the still classroom while the rain was falling outside. "Aw, you didn’t write that!" protested one of the boys.

"I did," said Margot. "I did."

"William!" said the teacher.

This is the same teacher who leaves the children alone when the sun comes out.  It is because she left them alone and did not stop them from bullying Margot beforehand that they bully her now.  The teacher’s neglect leads the children to their final cruel act of locking Margot in the closet so that she misses the sun.

Bradbury’s message is that all adults (and children) need to take bullying seriously.  It is not just fun and games.  Bullying can have disastrous consequences on both the bullied and the bullies.  After the children lock Margot in the closet, they are horrified at their own actions.  This is an incident that every child will remember for the rest of his or her life.