During my articles year, I was told by my "mentor" (I use those inverted commas for a reason) that I would "never amount to anything as a lawyer".

Let's just say when I won the State's best junior advocate award, two years later, I faxed him a copy of the newspaper article. Anonymously

But yes, it still sticks in my mind years later. Good on your DS for standing up to her. Her behaviour is unacceptable.
Yep, same thing with DH's teacher. DH was told he was crap at maths and would never ever be an electrician. It made him strive harder once he left school and he's now been an electrician for 13 years.

I agree what the teacher said should never have been said, but hopefully it will have a positive outcome for your son. And yay for him that he was brave enough to say something back.