Yes, this is a good phrase to use. 'I had some discipline trouble with my pupils at first, but now they're growing on me.' One word of advice : make sure that you get the stress right in the phrase. You need to stress the word 'growing' , but not 'on'. If you stress 'on' it will sound very strange indeed.

Nice subtlety by Su.Ki on the stress. Definitely on the 'growing'. I would use students instead of pupils because of the other use of pupil, especially in relation to growing. Your pupils (eyes) grow in bright sunlight. To avoid confusion you could also say 'I'm getting used to them' or more indirectly 'We are getting used to each other'. Said with a smile the last phrase would be a good example of classic British understated humor: your audience knows who is getting used to who and leaving it unsaid is a subtle joke. Generally I've always found 'growing on me' a bit awkward except in the context of art or music where the usage is quite natural. "I didn't like jazz at first, but it's growing on me"