All the people at the conference are mathematics teacher/teachers.?

Question

My English teacher said here "teacher" should be in singular form, but I think "teacher" should be in plural form.
Could you please tell me which one is right or better?

Answer 1

It should be "teachers" because that choice fits the sentence structure.

All-the subject
are-verb
teachers-predicate nominative

You would not state... All are teacher.

Therefore, you are correct if she did indeed say that teacher should be singular in form.

Answer 2

The s on mathmatics is whats throwing you. Since it is already a part of the word and not a pluralization, an s goes on both words