I also did speech therapy last year when I was 15. I think it helped a bit, but not too much. You should try to do it anyways; my therapist also did lots of adults. Also, rehearse saying common block words, even if you have to change them. For example, I commonly block my name, that starts with a T. So instead I just say something like "My name is T****". Saying some other words in front often helps, even if it might be a tad bit disruptive to role call, it still looks better than blocking. Also, instead of just saying "here", say "I'm here", "present", "right here", and so on. Might help. Lastly, I find that it helps my confidence SO MUCH if I tell other people beforehand that I stutter. That way people don't think that I'm mentally disabled or anything like that. At the very least, stay after class and tell your teachers so they know and maybe make exceptions.