The WIAT II writing portion was a persuasive essay, as I recall. Students tended to do well on it if it was a subject they found interesting. There were some points for spelling and grammar, but I believe content was weighted more than mechanics. I'm no longer giving academic assessments, so I haven't given the WIAT-III.
Fortunately or unfortunately, schools under NCLB are not judged by their mean or average test scores. They are judged by the percentage of their students who make the cut for "Proficient". Losing one brilliant student doesn't make much of an impact on that percentage, but programs targeted to gifted kids might just act as a magnet that would.
