Final answer:
In 'Because of Mr. Terupt', Peter is the one who threw the snowball at Mr. Terupt, which is a significant event that changes the dynamics of the story.
Step-by-step explanation:
In the book Because of Mr. Terupt, it was Peter who threw the snowball at Mr. Terupt. This incident is a pivotal moment in the novel, affecting the lives of all the characters and changing their perspective on many things, including their relationship with each other and with Mr. Terupt. The snowball incident serves as a catalyst for the events that unfold in the story, creating an emotional journey for both the characters and the readers.