Same situation here , I also used to get 80-90% in my academics but if i were not a stutter i would have gotten far better grades. But you are wrong here, You try to avoid interaction with your family and others because you think they will get annoyed. You think this, because now you have a reason to not talk and do not face the pressure while speaking. But, if you go like this and avoid everyone, Then you will never ever be able to cure stuttering. You can’t improve your speaking skills alone, That’s simply not possible. So, Push yourself , no matter what. While i am saying this, I myself cannot fully do it,but i try to.