I don’t understand why a teacher would say this. I often let people know for myself and not for them and I make that clear and own my stutter. The teacher telling you not to is just adding the potential of extra anxiety around it instead of allowing you to own it by saying something like: “before I start I just want to say that I’m a stutterer so if you notice, it’s not nervousness it’s just apart of who I am. If you have a problem with it, that’s okay because I don’t”.