I would say re-test. This same issue came up in one of my gifted parents meeting. The parents had the older child tested by a school psychologist or similar. The score came back bright but not gifted. For reasons I am not sure of a few years later the younger child was tested by a different psychologist that had done a lot of testing with gifted kids. The scores came back in the high gifted range. Based on the observations of the parents of their children at home they felt like the scores should have been closer so they had the older child retested. I think the scores ended up being very close. The general consensus of the group was that you should choose someone that specializes in testing gifted kids. The opinion expressed was that school psychologists generally are more used to testing for problems on the other end of the spectrum. I think as a parent if you question the scores then they very well may be off, especially since this is your youngest child and you have something to compare them to.
