My thought in that case is that the age of the child at the time of the testing might have had some impact. For instance, a 5 y/o who is tested on the WISC is likely to have a higher score than a 15 y/o even if the ability is the same. I say that b/c the 15 y/o is going to run into some significant ceiling issues.
So, for instance, the score at 5 when the test was newer might be lower due to the newness of the test and, at 10, it might be lower due to the age of the tester but higher due to the "oldness" of the test with those two things cancelling each other out. I hope that makes sense - just my random thoughts.
