The way you teach students

The plural is teacher in charge.

As in "there is one teacher in charge here".

Usually, the French word for teacher is "professeur". But in the old times, sometime they were using the word "maître" to designate a teacher.

A teacher (also called a schoolteacher) is a person who provides education for students.

"Teacher's Luncheon" means that only one teacher could attend. "Teachers' Luncheon" denotes the plural form, i.e. a luncheon for many teachers.