Interesting question, isn't it? You would think, not to say assume, that any math teacher would agree with the fact that zero is indeed a number. It is located on the number line between 1 and -1, you can add to it, multiply by it, divide (although the "real" answer would be undefined), or subtract from it and obtain a negative number.
This morning, my kindergarten daughter, asked one of the teachers at my middle school the question, "What is the first number in the number system?" She (the student) gave her (the teacher) the answer as being zero, to which this "eminent" teacher said, "No, it's not. Zero is not a number; it is a place holder." I almost spilled the coffee on me. The teacher left the room shortly after this conversation, and I tried to explain to my daughter why zero is a number.
At this point, I would like to hear from some of you, math teachers, about your position related to "zero". So, is zero a number or not? What is your final answer (if there is such a thing as a final answer on this)?