All teachers do that. Maybe he's just trying to cool your ego. You can't expect everything to be rosy in the real exam. Ignore it, and just focus on work. If you want a second opinion, ask another teacher to grade some work. In the real exam, the examiner won't know you and won't care. They have to go through hundreds of papers and won't care about your contribution! If you think you're doing great, just keep going, and ignore it. Try to be more proactive in lessons if it's really bothering you