Do teachers/professors refer to each other by their titles? I just began shadowing a high school classroom as part of a requirement to earn teaching credentials. The teacher I'm shadowing has a PhD and is referred to as "Doctor Smith" (generic name) by his students. I am not his student and it is the first experience I have in a classroom setting where the teacher is my peer; but, it still feels uncomfortable to call him by his first name. 

Do I call him "Doctor Smith?"

If he doesn't have a PhD, should I call him "Mr. Smith?"

When is it appropriate to call someone by their first name?
A good safe approach is to start out calling him "Dr. Smith".  Most likely he will quickly say "Please call me Fred" and then everything is resolved.