DD started to feel 'different' probably the same say she started with the preschool at 2.4 yr old.

By 3 she definitively felt different from others.

In her case this was not good at all, and I think this has contributed to her underachievement a lot.

Now I really do not know how to talk about the whole issue with her and how to get her out of the underachievement.

On a related note: did you see your kid/s as 'different' before your realized they were gifted? I used to think that, either DD was from another planet or the whole 'parenting books/web sites' were largely the biggest lie I have ever seen. When I read for example fun activities for toddlers I always thought 'uh uh this is not going to work with DD' (because she would do her own thing).