What are you trying to get out of testing? <-- this is the question to drive your choices.
I would think reviewing your school district's policies would be first priority. Check for acceleration request deadlines - often in February for the next school year! Check if they will do *anything* for children under grade 2 - many districts won't. If your school/district is not accommodating or understanding, there may not be much point in further testing.
I got blown off by the elementary school when my son was 4K-1st. They wouldn't come close to meeting his needs and refused accelerations because his "normal, typical" behavior. They interpreted his ADHD symptoms as being childish, low maturity and therefore no need for academic intervention. IQ and WIAT III testing didn't help me. I pulled him out of school, he accelerated 3 grades immediately and after a school-year with ADHD medication he was up to 5 grade levels ahead of his age peers. There was no way that the district could physically accomodate that without putting him in the middle/high school building. Even if testing would have convinced them to meet his academic needs, it wasn't physically possible.
