Depends if you're talking about teachers in school or not. In primary or secondary school you can call them Mr/Mrs/Ms X (delete as applicable). In secondary schools in the UK male teachers are also called 'Sir' and female teachers are called 'Miss' without their surnames (the female teachers were called 'Miss' regardless of whether they were married or not, it's just easier to say than Mrs. I guess.) This was by far the most common form of address when I was at school. There was only ever one teacher who got annoyed about being called Miss, and who insisted that we called her by her full name. Miss Taylor, I can still remember her name. Anyway... Outside of a school environment, say in a language academy or a university, basically when the students are adults and no longer children the teachers/lecturers are normally addressed by their first name. Teacher X isn't rude, it just sounds weird to a native English speaker.

Hi Sunny, I'm American, so my answer only applies to American students. We call our teachers Ms. Smith, Mr. Smith, Dr. Smith, or Professor Smith, depending on the situation. It's not necessarily impolite to call a teacher Teacher Smith, it's just not something we would do. Hope that's helpful! Dana

They usually call their teachers Mr/Mrs/Miss with their last name☺