blueskies - it can apparently be harder to score well as an older child. One of my children has been tested three times, another twice, we've used three different psychologists. The personality of the tester has had some impact, as have their health on the day and the particular test used. But for both children their VCI has not moved more than 3 points. Both girls have higher non verbal scores on the SB5, it seems to suit them better. My (more) 2e child has very variable WMI and PSI scores. Both children got their hightest scores with a gifted specialist that they both really clicked with... But fundamentally there is a certain level of consistency between tests and testers.
