Translation:When I said that the teacher doesn't know what he's talking about, I was sent home.
I think the English translation should be "When I said that the teacher didn't know what he was talking about, I was sent home".
It's slightly more natural, but the way it currently is isn't incorrect, and it makes it easier for learners when they come across the reverse exercise (English to Hebrew).
Actually I think it is incorrect. But I got it right the first time without thinking about it so maybe its worth keeping anyway.
The use of the present tense "doesn't know" instead of "didn't know" implies that the student thinks the teacher is wrong most of the time, not just on that one occasion.