I always think that objections to American-English spellings carry the distinct whiff of British imperialism. Using z instead of s seems pretty logical to me, as the letter is pronounced z in the words that raise hackles here and there. And, as I understand it, many words with so-called American spellings actually began their lives on this side of the Atlantic spelled the American way. Admittedly, it would seem odd to adopt American spellings here, and teacher certainly wouldn't like it. It should be a case of when in Rome, and just enjoy life.