Wow! Thanks for all of your stories! Really, the different points of view do help!
As an update on the Mr. Zero teacher:

I asked my DS today what kind of tone the teacher had used; did he think she was just teasing or joking. He said she had definitely used a harsh tone. Unfortunately, a mom whose daughter is in my DS's class emailed me tonight telling me some things her daughter told her about the teacher. Her daughter told her that the Mr. Zero teacher did not like my DS and most everyone knew it because the teacher was always saying something mean to my son. I know she dislikes him because he corrected her once. Left two messages for the principal to call me... nothing yet.

Dumbing down? I've mentioned similar to my son, but his concern to me was something I could not answer: "How do I know how simplified I need to make the conversation? I can't judge their intelligence. What if I make it so simple that I am insulting them for thinking they were that dumb?"
I have to agree with him. How do you know, at age 13, who you can speak to using your natural intelligence, and who do you speak to in "lay" terms? I am all about being kind and considerate to others; on the other hand, what message am I sending to my child by telling him your intelligence may insult others, so tone it down? When a beautiful, slender, young mom stands next to me (older and frumpy) at a PTA meeting, would it rub me the wrong way? Would I feel insulted? Should she tone down her beauty so she doesn't make me feel bad? LOL