I know others say there's no correlation, but from my own experience of meeting kids on the spectrum, they are very big. My daughter is on the 98th percentile. She's the tallest girl in her class, but one of the youngest. She's only 6 but looks about 8 or 9. I know only 4 other kids with ASDs and all of them are the tallest in their respective classes, by far. But, they are kids and who knows what size they'll be when they've finished growing. They might end up being small. My BIL is undiagnosed, but without a doubt has AS. My MIL says he was a very big kid and was often mistaken for older, but he's average height now.
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"We act as though comfort and luxury were the chief requirements of life, when all we need to make us really happy is something to be enthusiatic about." Charles Kingsley