Gender identity is your own knowledge or understanding of self as a sexed subject (male, female, or otherwise).
I know this is a while back @Tandora but you've been asked a couple of times. Could you explain what you believe one should be basing their gender identity on, in that case? What is the criteria one could use in order to identify it?
Bearing in mind, that this is about teachers' guidance, and therefore should be something that children can understand.
And, just as a heads up, I've never seen a single explanation that doesn't rely completely on rank sexism.
Or the old chestnut, that it's individual to everyone, and you can't explain it.
Which isn't what one would normally consider a useful concept on which to base laws, policy, protocols and guidance.