the world around him, and 2) the trials and tribulations of being a boy in search of his own identity.

One metaphor that occurs in the book is used to describe Holling's reverence for Mickey Mantle after learning of his death:

When gods die, they die hard. 

Holling is comparing Mantle to a god, even though he was a mere mortal.

There are also plenty of similes to be found in this book. Holding compares his experience of being pressured by his classmates to bring them cream puffs to the troubles of Antonio in The Merchant of Venice:

I remembered the death threats hanging over me like Shylock's knife hanging over Antonio's chest.

When Holling hands in a test five minutes prior to the end of the day, his teacher decides to correct it in front of him. Holling describes this with another simile:

"Stand here and we'll see how you've done," she said, which is sort of like a dentist handing you a mirror and saying, "Sit here and watch while I drill a hole in your tooth.” 

Similes compare two things using the word "like." In other words "the lights twinkled like stars" is a simile.

On page 4 of the book, the look comes over the teacher's face "like the sun had winked out..."   That's a smile.

Page 8 -- asking your sister... is like asking Nova Scotia...  That's a simile too.  Both of those use the word "like" to compare two things...

Metaphors also compare one thing to another, but don't have "like" or "as" in them. So the idea of your "mind's eye" is a metaphor. Metaphors are also used in sentences like "his attempts were just a drop in the ocean..."

One example of a metaphor comes in the first sentence of the book where the teacher hates him with "heat whiter than the sun."  This metaphor compares her hate to the sun.

The Wednesday Wars by Gary Schmidt is told from the perspective of a seventh-grade boy named Holling Hoodhood. Holling is rather dramatic, as noted in the opening line of the novel:

Of all the kids in the seventh grade at Camillo Junior High, there was one kid that Mrs. Baker hated with a heat whiter than the sun. Me.

His vivid language reflects his feelings throughout the novel, and he often expresses them through figurative language (note the imagery of the white-hot sun in the line above).

Imagery usually appeals to one or more of the senses, and Holling gives us plenty of imagery throughout the novel. Other examples of imagery include the following:

• "The chalk dust that didn’t get into my lungs flew and twisted with the breeze that curled against the first-floor classrooms, coating all the windows…." Note the use of sight, touch, smell, sound, and even taste in this example.
• Sycorax and Caliban "had hair the color of cardboard in splotches over parts of their bodies, but mostly they were just yellow and scabby skinned." If you find this description at all disgusting or creepy, Holling has done what he intended. He appeals primarily to sight and touch for this one.
• "So we sat in the half-dark, in our coats, in the cold." Imagine kids huddled in a classroom in the winter without any electricity, and this is how it might look and feel.

Metaphors are comparisons between two things which serve to help the reader understand or feel something more clearly. Just before the holidays at Camillo Junior High, teachers decorate their classroom doors with all manner of things, and Holling describes them this way:

The windows on the classroom doors became crepe paper-stained glass.

Holling uses a more compelling metaphor when he describes how he felt when his baseball hero Mickey Mantle proved to be rude and unkind. Holling says, "When gods die, they die hard." To him, Mickey Mantle had been a kind of god, and it was a hard thing for Holling to accept that his god was nothing more than a flawed human being.

Holling also uses similes to draw his readers a picture of how he feels or what he sees. When his entire class, even those he thought were his friends, threatens him relentlessly to bring them cream puffs, Holling compares that to something in Shakespeare's The Merchant of Venice:

I remembered the death threats hanging over me like Shylock’s knife hanging over Antonio’s chest.

Holling is also moved by beauty, and here he tries to express that:

It was sort of a holy moment, and the light that shone around them seemed to glow softly, like something you’d see in one of the stained glass windows at St. Andrew’s.

Figurative language is an effective way to help the reader feel what the character is feeling and experience what he is experiencing. Though he is only a seventh-grader, Holling is able to express himself through figurative language throughout this novel.

Holling Hoodhood is only in seventh grade, but he has a vivid imagination and an effective vocabulary. He is the narrator of The Wednesday Wars by Gary Schmidt and he makes his story come alive for his readers by using figurative language. 

Figurative language is useful because it utilizes the senses to enhance the meaning and experience for the readers. Your question mentions five specific kinds of figurative language, and I easily found multiple examples of each in the novel.

A metaphor is a comparison between two things, and in the following metaphor, Holling compares his baseball hero, Mickey Mantle, to a god. When he finally meets his hero, he is horribly hurt and disappointed. He describes it this way:

When gods die, they die hard.

The baseball legend was held in high esteem by Holling before this incident, and it was difficult for Holling to see him fall (figuratively, die).

A simile is also a comparison between two things; however, it uses either like or as to make the comparison. When Holling is being threatened every day in class, even by his friends, to bring them some cream puffs, he compares his experience to a character in The Merchant of Venice by William Shakespeare:

I remembered the death threats hanging over me like Shylock’s knife hanging over Antonio’s chest.

Hyperbole is exaggeration used for effect, and we should not be surprised that a seventh-grader demonstrates plenty of this as he recounts his experiences. (The Antonio and Shylock is a bit hyperbolic, as well, since Shylock was literally going to cut a pound of flesh out of Antonio and the worst thing Holling's classmates did is hiss a few words at him.) When he is trying to clean the rats' cages, Holling inadvertently traps Sycorax and Caliban. He looks down at them and describes what he sees:

They both turned their little black eyes toward me--bulging with demonic delight--and clawed hysterically at the bars that were hardly holding them from escape.

Obviously this is a frightening scenario for the boy; however, the rats are certainly not demon-possessed.

Personification is giving human qualities or characteristics to something non-human or non-living, and Holling often uses personification to create an effective image.

The day was still a perfect blue October day, as if it had been waiting for me since I’d missed it at lunch recess.

We know this is an example of personification because days are not capable of waiting--much as we sometimes wih they would. Waiting is a human characteristic which is given here to something non-human.

Finally, Holling uses onomatopoeia to add a sense of excitement and color to his writing, as it uses words to make sounds. Every time he is anywhere near the two rats, Holling describes their “clacking their yellow teeth.” Though it is perhaps unpleasant to imagine the sound, it is an effective use of onomatopoeia.