English Grammar
posted by John .
He is a math teacher.
He is a Math teacher.
Do I have to capitalize Math or not? are both OK?

The only time you capitalize the M on "math" is when the word is part of the actual title of a course. Here are some examples:
He is studying algebra.
She is enrolled in Algebra I.
They are working on their math homework.
They are taking the Discrete Mathematics class.
So ...
He is a math teacher.
He teaches Mathematics IV.
She studies Math IV.
=)