This is a near-duplicate of the post here.

I will post the same response that I posted in that thread:
Originally Posted by indigo
Many gifted children have strong interests from an early age, which may lead them to take lessons in that area of interest, outside of school. Someone who has previously taught your child may have noticed their level of intensity, deep questions, amazing connections with other material, etc. This may not necessarily be a teacher of an academic subject; these characteristics, behaviors, traits of the child may be noticed by a teacher of a musical instrument, swimming, dance, horse riding lessons, whatever your child has been interested in and motivated to learn about.

Just my 2 cents.