I disagree. The grammatically correct form is "as John and I (were)" where "were", "were in", etc. are optional continuations. The answer "same class as John and me" is grammatically incorrect, though tolerated informally. It is similar to: "Who wants ice cream?" "I.", which is the correct answer and is short for the (optional) "I do". However, almost everyone will say "Me."; not only is the latte