Serving in my position as a mathematics specialist, it is, indeed, important to know the content of mathematics, but I think this second part of this statement - "understands HOW TO TEACH the content to students - is where I am able to truly be an instructional leader/coach. It is one thing to understand the mathematics involved, but it equally (if not more) important to understand the components of quality instruction that are required for students to obtain a deep understanding of the content taught.