My son turned 5 in December as well. We tested him on the SB-V at 4 years 9 months and the WJ-III at 5 years 1 month.
IQ testing for us confirmed what I already knew--that DS was gifted. He actually scored higher than I expected though. I do think his scores are accurate though. In the last few months my son has made academic leaps and bounds. Based on his scores we changed him from a preschool/daycare to a Montessori school. I think that change in learning environment alone has really helped my son. I honestly don't know if we would have made that change without having had the testing done. It was the push I needed to advocate stronger for my son.
The achievement testing was only done to qualify for DYS. It did give my son very high math scores but I do belive they were accurate as my son seems to pick up math very easily. The WJ-III at his age didn't require him to solve multiplication or division problems for a high score (which he could have done). I guess the inflation may be because 5 years old aren't expected to read or perform mathematical operations. When they can, obviously their scores will be higher.
I also have an almost 4 year old daughter (June Birthday) and an 21 month old son and I don't think we will test them until at least the summer before K or 1st grade, if needed. At this point I doubt my daughter would cooperate with a stranger whereas my son had no issues with the tester. He loved the testing process.
