I don't have much experience with the gap question - my son's been subject accelerated for 3 days now and did have vocabulary gaps that freaked him out, but once terms were defined things seemed fine. So far!

But on the testing question, I actually came here intending to post a pro-testing thread b/c of our experience with the school. It's awful, dreadful, that some people are so innumerate as to not understand what the results mean! But if they do, it's soooo nice. We've been playing this 'try to get the school on the same page as us' game for more than a year. It's been so frustrating, and clearly they didn't feel the need for any follow-through, ever. They were defensive and hostile, and we were doing our best to be careful and cautious and never ever ever say the 'g' word.

Then my son had a complete sobbing meltdown in class and they couldn't stop him. This freaked them out, as our repeated "our son is increasingly unhappy and tearful about school" letters did not. We had a meeting get scheduled REALLY quickly then - what a change. We walked in there and the principal started off with what sounded like the "your son is under a lot of pressure from you" talk. And our psychologist, that we tortured ourselves over deciding to hire, whipped out the test results, slapped them on the table in front of all the school people. It was all quiet for a bit, then, some "wow"s were heard. DH and I were just SO loving that. They then recovered pretty quickly and said "well, of course we all expected this." (hah). But the beauty of it was that it completely stopped the hothousing "he's not as smart as he thinks he is" comments, and has got them, however temporarily (though I hope it'll be permanent!) willing to think creatively and flexibly about getting our son to a place where he's learning in school. They changed their stupid grade-level only library checkout policy, his teacher got him a bunch of hard books to keep in the classroom to read, some of which were on math and science, which was brilliant of her. And despite their seeming to think it would be overwhelmingly hard to have him go to a different classroom for some subjects, he's been accelerated in math. So he has a math challenge, books that are both interesting to read and teach him something, and, maybe most important, the feeling that they finally understand that he's smart and that things will get better, in ONE WEEK after more than a year of talking about this problem. They didn't listen to us one bit, but the test scores? That made all the difference. It makes me wish I'd tested him as he started school. I think that's probably not necessary as long as there's no problem and your child is happy...but if there's a problem, oh, how it helped us. (and it helped us personally, too, with the knowing what we're dealing with thing, and the not feeling crazy thing).