What does "He sucked the life out of his students" mean?

Question

Because my band director said this about one of my teachers sophomore who really was a complete A** hole because he was always putting me down and I always came to the band room close to tears. anyway my band director stood up for me that year, and the beginning of my junior year my mom and him where talking about how hard of a year I had last year and he said that to my mother . "Mr Green sucks the life out of his students." So I was just wondering what that phrase mean?

Answer 1

too hard one them

Answer 2

To me it means this teacher would not allow students to state their own minds about different topics.  A teacher who does not allow a student to think for themselves or belittles them when they come up with different ideas.

Answer 3

I think it means he was a kill joy