I'd say that whether you should re-test or not depends on a number of factors. Here are a few off the top of my head:
1) What are the differences between the two instruments, and how significant are they?
2) How much time has passed?
3) Are there any significant changes/new challenges you've observed in your child that additional screening would help identify?
As for the first one, I'll let people more familiar with the differences between the two tests answer it.
As for the second... probably enough. My school system mandates re-screening for gifted services every three years (unless both the school and the parents agree there's no need), so you're right on the edge there.
As for the third, I'd say that unless you or the psychologist have a strong reason to suspect a learning disability, I wouldn't worry about it.
It's always possible the psychologist is offering this as a way to collect more money.
Last edited by Dude; 12/19/11 10:06 AM.