I am starting to get confused. From what you have said, your current extension of stay is based on your last arrival in Thailand which you made with a tourist visa.
What is this school you are talking about? Is it a school at which you are studying, or is it a school at which you will teaching after getting the necessary paperwork done?
What exactly is the "volunteer visa" your old passport? Never mind. As your current permission to stay is based on your tourist visa entry, immigration will make no note of this "volunteer visa" or any other visa in your old passport.