Dave standing up to Mr. Neck's xenophobic remarks.
The turkey-bone sculpture, with a duct-taped Barbie head and the bones shaped into a tree sculpture. Mainly because Mr. Freeman and Ivy intuit the emotions presented within the piece.
Melinda refusing to help Heather after the latter has dropped her in favor of more "popular" friends. Becomes a "Reason You Suck" Speech in the film.
Though it earns her a D on her assignment, Melinda finding a loophole to giving an oral report, and Dave helps. They pass out copies of her report to the whole class and plan to have her stand for the required duration of her presentation.
Melinda playing tennis against the class athlete, Nicole. While she ultimately loses, it was a close match, which is a testament to her own skill at the game. She even wins Nicole's respect in the process.
Melinda writing Andy down as a guy to stay away from on the Bathroom Stall Graffiti in the girls' room, which leads to a flood of responses from other girls agreeing with her.
In the movie, after mulling over what Melinda told her (despite not believing her initially), Rachel considers that perhaps her ex-friend really is telling the truth about her boyfriend. The next time she sees Andy, she instantly breaks up with him.
In the book, it's an Offscreen Moment of Awesome where Rachel not only breaks up with Andy during prom after he makes her uncomfortable with his hot and heavy behavior, but also calls him out as a predator in front of everyone. To top it off, she leaves a cremated ash pile of all the gifts Andy ever gave her, right in front of his locker the next day. Even Melinda is impressed and can't help but derive a little schadenfreude at his expense, with her inner narration calling him a "scumbag".
The climactic showdown between Melinda and Andy. Andy, angered at how Melinda's actions led to Rachel exposing him as a predator, tries to attack Melinda and even rape her again. But this time, Melinda is able to fight back—she splashes a cup of cleaning chemicals into Andy's face to blind him, smashes the turkey bone sculpture against the mirror, grabs a large shard, holds it to his neck, and firmly says, "I said no."
And then the girls on the lacrosse team break the door down and see what's happening and come to Melinda's defense, and they all repeatedly call out Andy and tell him "everyone knows what you did", all the while ignoring his pitiful cries of pain.