I have a 10 yo who was like this, and I started off cross that the school were limiting him and forcing his pace to slow down etc.
He's now in year 6 and with some good teaching, he has gradually learnt actually that being the quickest with the answer and shouting it out isn't the only skill he needs to get on at school. We are very grateful that the school are also helping him to learn manners, consideration, social awareness of the different needs of others, respect for authority etc.
Because now he's about to hit secondary school, I absolutely DON'T want him to stick out because he's the smartarse. He is learning to be a social genius rather than a know-it-all. Not hiding his light under a bushel exactly, but remembering some modesty and knowing when it is appropriate to shout and how to tell the teacher when he thinks she is wrong.
I am SUCH a liberal namby-pamby that I could never imagine these words coming out of my fingers mouth when he was little. But your first born is used to being heard first, used to getting your full attention, used to being praised for being so very clever. Mine was. And so at school where they simply can't have such one on one attention it becomes very hard.
Balance is the key - a good working relationship with the teacher and strategies to keep him occupied (we always gently suggested they give our first born extra responsibilities in class - worked a treat), with gentle teaching that he needs to think about others, AND protect himself in social situations, while getting recognition for his skills. IME it gets easier if they group/stream later on, if there's a G&T programme and if you get good teachers who don't mind kids knowing more than them