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I'm a gifted child myself and it sounds very much like your son is too. He shows great capability and I suggest you take him to an appointment with his school and perhaps get an IQ test.
By the time I was 6 I was able to multiply/divide by 2, 3, 5 and 10 and do addition and subtraction sums up to 100.
I was also very curious about the world, enjoyed the company of those older than me or simply being by myself.
Hope this helps!
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One strategy to use when a child gets too far ahead of the curve
Gifted Kids with learning problems... The Twice Exceptional Child.
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