Calvin is dealing with an environment made up of many, MANY, entity theorists. They all look at his personal characteristics, his curiosity, his humor, and determine him to be a "bad" kid. They don't look long enough to see how smart, fun, and creative he is. He makes whole worlds in his mind and creates a space where he is not seen as the bad kid.
Calvin does not feel motivated or safe enough to learn the content that is being taught to him. Not only does he view the content as useless and school as a waste of time, his teachers and peers all make him feel unsafe. His teacher, instead of giving him tangible feedback, simply tells him to work harder instead of giving something he can actually change. She has said openly to his face that she can't argue with the statement of him being in a state of denial. When does ask questions and appears interested in class, his questions are shut down and he is punished. He asks how things will be beneficial to him in the future and no one feels the need to answer his questions, including his parents. Why would a child do something that won't benefit them in any way?
Often, in the comics, his teachers, parents, and classmates berrate him: calling him stupid and insulting him in other ways. He also gets bullied. Despite his witty comebacks, he is cast out by his community and is isolated. His only comfort is Hobbes. To Calvin, it is the world against him.