From my experience as a parent of much older kids. (Mine are 19 & 14, and I've known many other kids their age.) There are some toddlers that are just obviously gifted. They read incredibly early, or pick up an instrument, or show amazing mathematical ability. And others that don't really bloom and show until they are 7 or 8. Kids are all different and it's very hard to test preschool age kids for giftedness.

For example my son was one of those obviously gifted at 3, while one of my BF's girls wasn't interested and didn't really read well until the beginning of 2nd grade and then she just bloomed.