When I was very young (about 6 roughly) my family decides to move Scotland from Germany due to my dads work. Only problem was that I couldn't speak a word of English and pretty quickly got known as the kid that doesn't speak, at my school... I picked up English pretty quickly, but I pretty rarely spoke and only when I had to (same sort of think where I would deal with teachers but pretty much avoided my peers). I hated having eyes look at me when I got asked a question, but I feel the worse thing for me was potentially answering the question wrong... So I pretty quickly found out that the best way to go about this was just to say "I don't know" and the teacher would move on and eventually realise that I don't want to be asked. I did have a French teacher that did the worst possible thing though, she took it as an excuse to pick on me, that class turned into literal hell and was one of the only times where I actually completely failed an exam... I couldn't concentrate in that class, every waking moment was me living in panic, that the teacher was going to ask me some question that I couldn't answer. And it was pretty much impossible for me to think of the answer in front of the whole class, so it just ended up being a dreadful cycle... with a Lovely grade D to finish it all off :/
So I pretty much got picked and bullied on as well, for being quiet and on top of that the casual nazi "jokes" probably didn't help either... Pretty much have no self confidence now :/ Worst part about the bullying was that once I finally had learned English I could actually defend myself in theory (not that I ever did) but when I couldn't speak English how was I meant to... Thinking about it now it actually seems really cruel, but hey, kids... What you gonna do...?
I managed to make some friends during school and I was happy to have conversations with them, but anyone I didn't know I generally stayed clear off (either outright ignore them or give some sort of hand signal if it was a question for directions or something)... I still do that now to some extent (actually somewhat surprised how I manage to make friends in he first place...?).
What is it with schools and forcing public speaking on you... I don't get it, it's the worst possible thing on this planet, yet they force you to do it anyway? I had to do a few over the years, got worse with everyone I had to do, and I got the usual your just shy speech as well, almost just started to assume it was normal to feel like your having a heart attack while giving one... I had to do one on "an embracing moment in your life" ... I honestly don't know if there's a worse topic than that?
So I guess I wasn't completely mute as in your case, but I definitely stayed quiet when possible though... I do feel like the anxiety issues I still have now though were caused by us moving, I was pretty much forced into the centre of attention, the very place I try to avoid as much as possible... I should point out though that I don't blame my parents, I've never really told them what an ordeal school was for me and I'd rather not make them feel guilty about it either.
I made it to uni though, and I now manage to answer questions and generally feel more comfortable in those sort of settings... Generally happy to speak with people I don't know as well. Public speaking is still an issue though... Almost collapsed the last time I had to give a presentation :(