my situation is almost entirely the same as yours but i'm just 16. from what i've experienced, you really need to not care and say what you want or need to say. i would recommend talking to your teachers about your stutter for them to be more understanding and lenient about grading participation for you. confidence in speech and not caring about your stutter is going to be really beneficial for you, but it's the hardest thing to really accomplish. for starters, i think take a deep breath before speaking, or breathe while you speak. if your friends laugh at you for stuttering, either confront them about it or make new friends; they would make you feel more insecure about your stutter. for words that start with B, D, L, T, i really try to enunciate the letter before saying the rest of the word, it sounds weird sometimes but it helps. if you really can't say it, either have a synonym for that word or take breaths and try your best. it's really not easy, but you have time and opportunities to practice your speech. ​ TLDR: comfortableness with your stutter is really key, talk to your teachers about your stutter and lenient grading, deep breathes are needed whether you're going to speak soon or stuck on a block, if deep breaths don't work for a block, have a synonym or try your best to spit out