Cat,
One of my DSs took SCAT at age 6 (second grade) mid year. I don't know how the awards & stuff work, but he really enjoyed it and finished very quickly (nerve-wrackingly so).
Didn't have any further advice about it, except that you should do it when it's convenient for you/him (for us, it's a 3 hr drive each way to the test center, but that's not true for most people). I picked mid year because there's a lull of learning--it's mostly holiday activities, preparing for big State Test crunch, no soccer, etc. Good time for enrichment with a nice above-level test.
Cym
