<p>I am going to add a pair of more current contrasting grad-student anecdotes:</p>
<p>My daughter -- not a math person -- was taking a calculus class taught by a grad student. She never loved calculus -- she was thrilled to get through the class with a C -- but she thought he was a wonderful teacher, who consistently "reached" her and got her to appreciate the intellectual content and importance of what she was learning, and who convinced her that she could pass the class and didn't need to drop it when she fell behind for a while.</p>
<p>One of my cousins recently got his PhD in math from an Ivy League university. For a number of years, he had to teach undergraduate math classes like that my daughter took. He learned very quickly that he had very little interest in teaching undergraduates. This is what he said about it: "About the only enjoyment I get out of teaching is seeing the students' slow, inevitable progression from initial happiness that they have a native English-speaker teaching them to the sad realization that they would have been much better served by a teacher who didn't know English but who gave a **** about them."</p>