There is significant interest around the world in all issues involving the recruitment and retention of students in mathematics and sciences at all levels. Because of this there is great need for programmes that focus on providing well-prepared and effective teachers of mathematics and science at all levels. In this article, we present sample programmes in the US that focus on the professional preparation of mathematics graduate student teaching assistants. We give a detailed description of one such programme along with an assessment of its effects on the graduate students' teaching practice and philosophy. (Contains 6 tables.)