Classe and professeur or éducateur
The possessive form for 'the classroom belonging to your teacher' is your teacher's classroom.
salle de classe
I can say without a doubt, It is when the teacher's out.
l'enseignant!!
professeur
"Le bureau" is commonly used. If you want to be really specific, you can say, "le bureau du prof (the desk of the teacher)," but that's probably overkill.
To say "the teacher is friendly" in French, you would say "le professeur est sympathique."
the teacher chair is called 'la chaise du professeur' in French.
a music teacher is un / une professeur de musique in French.
l'enseignant(e) a....
mme.
"enseignante"