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... reading... books & ...studies... does not make me an expert in gifted education.
I'm only an expert on one single child.
When you are advocating for your particular child, you are the expert on the subject at hand (your child).

IQ and achievement test results can be helpful for showing your child's departure from the norm. Portfolios or samples of work which are not age-typical are often helpful for purposes of illustrating your child's unique approach and interests as compared with age-mates. These things can help powers-that-be at a school or district to see the same advanced abilities which you observe in your child, and therefore help them better gauge an academic and curricular fit.