We did SB-5 at 4yrs 9 months and the WJ-III at age 5 yrs 1 month. We didn't wait until because we were trying to determine where my son should go to school. Personally I needed a good reason to pull my son from daycare and pay the much high Montessori tuition. I also think that it will help us get an edge to skip K. My son also hit many ceilings on the SB-5 but it did us great insight on his strengths.

Crisc