Extended norms:
When they calculate the scores the come up with the standard scores that stop at 19. The score needed to get a 19 might be say 30 questions right, but there could be 40 questions on the test. So, they call getting the max score when evidence shows you can do even more it's a ceiling effect. The implication being there is more they can do, with having more than one subtest at the max, it more strongly implies that. So, they recalculated for kids who hit the ceiling to see just how much further out their raw scores would take the standard score.
GAI means General Ability Index. It focuses on the two areas (verbal comprehension and reasoning) that fit closer to a classic sense of intelligence vs. memory and processing speed that the other two (WMI and PSI) test. A significant proportion of gifted test takers have significantly lower WMI and PSI scores. When it comes to the question of what sort material and rate and complexity a kid might learn better, GAI is more meaningful.
