Depends. In class I usually call him "Guru". Out of class or introducing him to others it's "Steve".
When we were teaching we went by our first names.
Other teachers are usually referred to by name. If they want to be referred to by some other title I tend to oblige out of courtesy. I say "tend to" because some people abuse it. Anyone who requires an ornate show of groveling respect, anyone with no gray in his beard who demands to be called "Master" or anyone at any age who wants to be called "Grand Master" will have to look somewhere else. I have enough trouble keeping a straight face.