Clarisse thinks education is incredibly important. However, she does not go to school because in this society, people are not taught to think for themselves. They are taught to be automatons. So, Clarisse won't get anything of intellectual value from the schools in this society. When Montag asks her why she isn't in school, she says she doesn't "mix" with the other students. She complains that her school's idea of education is pointless:
But I don't think it's social to get a bunch of people together and then not let them talk, do you? An hour of TV class, an hour of basketball or baseball or running, another hour of transcription history or painting pictures, and more sports, but do you know, we never ask questions, or at least most don't; they just run the answers at you, bing, bing, bing, and us sitting there for four more hours of film-teacher. That's not social to me at all.
By this definition, her school consists of students being preached to, probably brainwashed. They have TV class to encourage them to become addicted to the parlour shows. They transcribe history, which means they copy the school's warped version of history. The students are never encouraged to ask questions or think for themselves. They are also taught to be violent. Clarisse is against this type of "education." She would much rather question things and she does this in conversation with her family and with Montag. Note that Clarisse takes an avid interest in everything around her, from rain to dandelions. She wonders what makes people happy. She doesn't "mix" in school because she is a free thinker. She is quite interested in valuable education but not the mind-numbing instruction provided by her school.