What would be the term in English for the teacher of a primary school...

[Greek_Warrior]

...class who teaches mainly in that class? For example I've heard of the term 'form tutor' for the teacher who is resonsible for a form in middle education. In Primary education, what would you call the teacher that teachers the fundamental lessons in a certain class and is in charge of that class? Can we say class tutor? In my language we use the word class and not grade, so I need something that relates to the word class. In Greek we say Responsible Class Teacher, but I don't think that sounds right in English. Please help...
In need something to contrast against being a teacher that may teach secondary lessons in various other classes of the same school.