My speech therapist has a client who fled from a warzone and developed stuttering after witnessing a massacre, so for him it definitely came after a serious traumatic experience. Whether he had a preexisting tendency for stuttering that never manifested or really mild symptoms which he never noticed until the trauma is unknown. But my therapist was pretty confident about that diagnosis. Suttering for most people does not originate from a traumatic experience. In most cases it's hereditary, genetic and manifests neurologically (I guess what you mean by developmental). That's the current scientific consensus, although much remains unknown. Acquired, either from brain injury or extreme trauma only account for a smaller number of stutterers. At least according to my speech therapist. This doesn't mean that for you it couldn't be caused only by emotional abuse, but overall it's less likely. One's emotional and mental state can significantly influence stuttering. You probably already had the predisposition for stuttering and started showing noticeable symptoms due to the stress and bad experiences from the teacher. The teacher picks on you, you stutter a bit, the teacher picks on you even more (such teachers like to pick on the weak), you stutter more, etc. But maybe it would've manifested regardless of the teacher. There's no definitive answer in hindsight. Nevertheless, being bullied by a teacher surely had a negative impact on it either way.