Yes, that's true ! I'm French, and I heard "proviseur", not "professeur" ! "Proviseur" in English is "headmaster" or "principal".
In fact, in France (not applicable to Quebec, Switzerland or belgium, school teacher are officially called "professeur des écoles" (litteral translation of school teacher) but most of the time they are called "instit'" for "instituteur/institutrice" they former name and called by the pupils "maître/maîtresse" after, in collège and lycée, they are called "professeur" (or "prof") and when speaking to them "Monsieur/madame". In university there is the "Maître de conférences" and "professeur des universités" and only the latter have the title or professeur, but most of the time, people are still talking to them saying "monsieur/madame"
Yes, "professeur" is the first translation for "teacher". Students have "professeurs" from the age of 11, each with their own subjects (French, English, history & geography, maths, etc.) until the age of 18 (end of high school) and beyond in universities or specialty schools.
The British would say, "I am a teacher." A professor is a senior lecturer.