First of all, just so you know, depending on which state you live in, you might be able to opt your kids out of having to sit through this bullshit. Check out United Opt Out or FairTest for more information. If your kid has an IEP don't just take the word of the school district that he or she MUST take the test, that might not necessarily be true.
Anyway, I haven't opted either of my kids out because they both don't give a shit. If either of them ever for a minute showed any sign of distress about it, I would pull them in a New York minute; in California all you have to do is say "I would like to opt my kid out" and BOOM. All done. Administration will tell you that you can't, but they would be wrong.
That said, here's the conversation I had with Child 2 as he was getting out of the car this morning. I'm proud of us both:
Me: "How are you feeling about the testing, are you okay?"
Child 2: "I'm totally fine, because the tests are frickin meaningless. What's the point of being nervous about something that's frickin meaningless?"
Me: "That's right, there's nothing to worry about. But some of your friends might be nervous, so tell them what you just told me. And make sure you say 'frickin'."