^what? That's awful and unacceptable. If a teacher said that to my child I would complain. I understand that tough talking can be a great motivater but there is a way to do it that doesn't come off as just putting someone down and taking the belief out of them. Some people aren't tough enough to take on tough talking as a challenge and it will just tear them apart and they'll believe they won't amount to much.
If those teachers are so unhappy, leave, don't take your anger out on kids.
I know kids especially on high school can be a nightmare but that's no excuse.