A message of “All Summer in One Day” is that the root causes of bullying are jealousy and fear. Margot’s classmates are jealous of her and uneasy about her insistence of the existence of a strange (to them) object: the sun.
The classmates cannot conceive of the concept of sunlight, having been raised in an environment of perpetual precipitation:
this was the way life was forever on the planet Venus, and this was the schoolroom of the children of the rocket men and women who had come to a raining world to set up civilization and live out their lives.
Like all human beings, they have not control over the circumstances of their birth and upbringing. They cannot help being born and raised on Venus by parents seeking a new life away from Earth. In contrast, Margot had the privilege of being born on Earth. Her classmates are especially envious and resentful of her because
the biggest crime of all was that she had come here only five years ago from Earth, and she remembered the sun and the way the sun was and the sky was when she was four in Ohio. And they, they had been on Venus all their lives, and they had been only two years old when last the sun came out and had long since forgotten the color and heat of it and the way it really was.
Therefore, Margot possesses specific, tangible memories of the sun and its positive qualities (e.g., warmth, luminosity, and life-giving powers that produce flowers) that her classmates sadly lack. Instead, the only time when they experience fleeting memories of the sun is at night when they are sleeping. Unlike Margot, they cannot even imagine and enjoy the warmth, light, and beauty of the sun when they are awake. Upon waking, they hear only
the tatting drum, the endless shaking down of clear bead necklaces upon the roof, the walk, the gardens, the forests, and their dreams were gone.
The classmates also are jealous of Margot’s implied wealth and love from her parents.
There was talk that her father and mother were taking her back to Earth next year; it seemed vital to her that they do so, though it would mean the loss of thousands of dollars to her family. And so, the children hated her for all these reasons of big and little consequence. They hated her pale snow face, her waiting silence, her thinness, and her possible future.
Margot’s parents prioritize their daughter’s health and well-being over money and convenience. Whether or not the loss of so much money poses a hardship to her family, the fact that her parents are willing to sacrifice money and opportunity to return to Earth for Margot is significant. She has a “possible future” of potentiality and escape, while the classmates are trapped on Venus.
Fear of the unknown is another cause of bullying. The classmates seem unsettled by Margot’s claims of a sun. Even though a teacher compares the sun to something relatable, like a hot lemon, they cannot understand and thus doubt Margot’s authorship of her poem:
I think the sun is a flower,
That blooms for just one hour.
In order to control his fear of the unknown, one classmate denies the existence of it. When Margot insists that the sun will appear, the boy tries to shut her down while haltingly trying to garner support from the other classmates:
“You won’t see nothing! ... Nothing!” he cried. “It was all a joke, wasn’t it?” He turned to the other children. “Nothing’s happening today. Is it?”
They all blinked at him and then, understanding, laughed and shook their heads.
The only way the bully can take any anxiety out on Margot’s claim is to undermine it by turning it into a trick.
“All a joke!” said the boy, and seized her roughly. “Hey, everyone, let’s put her in a closet before the teacher comes!”
The classmates control Margot not only verbally, but also physically by shoving her into a closet. Their source of fear of strangeness—Margot—is extinguished. They no longer have to hear or see her.