Celi Trépanier, Author, former public school teacher, homeschool mom and a passionate advocate for gifted children
When to test for gifted identification will depend on the school your child will attend. In what grade level does the school's gifted and talented classes start? If the gifted program at your child's school does not start until 3rd grade, then having her tested the year before would be appropriate, but normally schools provide this testing.
Another consideration is the characteristics or behaviors you child is exhibiting now which would lead you to believe that she may be gifted. If she strongly exhibits gifted behaviors such as having taught herself to read by age 4, large, advanced vocabulary, intense emotional sensitivities, insatiable curiosity and other advanced cognitive abilities. There are many gifted traits checklists on the internet you can check out which are more detailed than what I noted above. Here is one you may want to check. If you feel strongly your preschool child is gifted, then you can opt for private testing because it is often helpful to know before a child enters school if they are in fact gifted.
Gifted children have many advanced intellectual traits, but they often have unique social and emotional needs which can pose challenges in school. Being aware of this and prepared is always a good thing!