Why is Mitt being so dismissive with a teacher in this round table discussion?

It was Mitt being Mitt. Basically, he just rejects anything that interferes with his world view and that includes facts. The fact that he was so rude about it was also typical of his behavior, despite the fact that the teacher was telling the truth.

He was an average student in college as well or he would release his transcripts. He's still average. He is the worst President in possibly our history and history will prove that out whether he is re-elected or not. This country is on the brink of catastrophe and I'm not sure why people would want to continue down this path.

If you're going to be Commander-In-Chief, he's going to have to learn to have everybody in his groups speak only when spoken to. At least that's what Romney seems to think.