So not to be crude (and to covertly or not so covertly hand you a soapbox and podium, and one of those pointy things teachers point with) what exactly is the difference between a person who isn't speaking because they really are shy and selective mutism .. is it just some new label psychologists and psychiatrists want to label people (especially children) with so they can get yachts faster and we can become a medicated unthinking society ?
Feel free to teach and preach away (and to take pot shots at me for being an ignoramus I could have wiki-d but the information will probably be more informative coming from someone who has dealt with it first hand)

You walk around like you're oh so debonair
You pull 'em down and there's really nothing there
I wish you would just be real with me