I think the word your teacher is looking for is, indeed, "classic," not "classical." I would conjecture that he or she is using "classic" to refer to works of literature generally revered and thought of as "great" in one sense or another by the literary community, and are also considered "acceptable" by the school system.
I truly dislike the idea of "classic" literature as is usually presented in high school, though, due to the second part of my conjecture. Too often, it's the same ol' boring books with a few good ones thrown in. I know that's really just my opinion, because I'm not particularly fond of lots of the authors I was taught. (Some of them, on the other hand, I loved dearly, like F. Scott Fitzgerald.)
It's not so much that I consider the majority of books taught in high school unworthy of study therein, but more so that I find it a fatal flaw that there are many, many great writers that are well-respected and truly made a deep impact on literature that the school system generally ignores. These include such writers as Kafka, Kerouac, Ginsberg, Camus, Pynchon, Borges, Beckett, Eco, Joyce, Marquez, DeLillo, and so on. Now not all schools ignore all of these, but for the most part, the great works of literature produced by writers like these are generally left out of the English classes. I have to ask why, as all of these writers certainly have as much, if not more literary merit than some of the authors forced upon me in school. My personal theory is that the American school system is simply afraid of the ideas presented by many of them, and prefers to stick to "safer" ideologies like Orwell's "totalitarianism is bad" or Harper Lee's "rape is bad." What do other people think of this?