I agree that it seems like someone should have the data showing whether there was correlation between the test scores and subsequent performance, but I sort of doubt that the party suing has access to that data. I've been wondering if that part of the complaint is based on a report that came out perhaps a year ago (year and a half?) that looked at students who fell on either side of entry criteria for selective programs. Remember that? It found that there was no benefit to the students who gained entry, IIRC. (I might very well not remember completely correctly!) That's the only report that I recall seeing that links selective program entry test score and subsequent achievement, but maybe there is more information out there somewhere.
A thread "Are gifted education programs a waste of money?"
http://giftedissues.davidsongifted..../all/Are_gifted_education_programs_.html discussed such research.