I think you have it right in your post. It happens when you are under stress, feel rushed, or when you get caught up in your anxious thoughts. The techniques that sometimes work, don't work. The truth is that fear changes what our bodies can do. Think of walking on a balance beam. If it's on the floor, no problem. If it's 15 feet in the air, suddenly you can't do the exact same movements you did on the floor. What has changed? The fear of falling. Fear affects what the muscles can do. Are you working on the fears, anxieties, and thoughts in your speech therapy? Learning how to turn the volume down on the racing worries and self-judgement and time pressure goes a long way toward making your stutter easier and less of a big deal, even if it doesn't go away entirely. It can take a long time to get a handle on fears about stuttering, but middle school is a great time to start. What you have to say matters, and other people care less about stuttering than we think. Good luck!