I'm in my early 70's now but I would tell the teachers to NEVER, under any circumstances, interrupt a stutterer, for any reason. The negative experiences are still burned in my memories, so much so I told of them in a Canadian documentary on stuttering. I was always being given time limits, which of course made my fluency worse. But the worst was the teacher who pulled out a stopwatch and then said times up and gave me a bad grade on that oral exam. Another, during an oral exam, every time I blocked on a word, would say it for me, then gave an almost failing grade( I single handedly was responsible for getting that teacher fired) It felt great .