I'm no expert, but yes, Dazey, I think that has a lot to do with it. They learn differently, and regular classrooms often don't meet those needs.
I think even the achievement tests themselves often aren't written to make good sense to a VSL kid. That means that VSL kids might not perform as well as they could if they were given a test that met the VSL person where s/he is, intellectually speaking. Just like I wouldn't do very well on a test given in Portugese, VSL kids don't show what they can do as well if given tests that were designed for non-VSL kids.
