I don't mean to slag off Deboarah L. Ruf personally. I haven't even read her original research or book, and plenty of what she says is common sense.
But the way her ideas have come to dominate thinking about intellectual giftedness, especially among online American communities and increasingly abroad -- is just plain unhealthy.
She's an experienced school teacher, trained academic (to PhD level), parent herself of "Gifted" children and she self-identifies as "Gifted". Her PhD focused on the early identification (testing methods) for Gifted children. In 1999 Ruf started a business called Educational Options, which offers services to help identify and meet the needs of Gifted children. Ruf wrote a best-selling book for mainstream audiences about childhood Giftedness: how to identify it and how to help children with it. She writes online and newspaper articles about these and other aspects of Giftedness. Her ideas and research now pervade most discussions of intellectual Giftedness (eg, see discussion on NAGC, or description of her visit to Australia.).
I was identified as "Gifted" in the 1970s, I went to a public school in California with a special programme for us "Mentally Gifted Minors" (utterly rubbish, and I was badly bullied there too boot). Two of my children appear to be on the "Gifted" spectrum (as defined by Ruf). But more important than any of that, I am an ex-university inter-disciplinary academic, so I have a habit of looking at any research -- especially social science research -- rather critically.
I feel very suspicious of the way Ruf's paradigms (or perhaps distorted versions of her paradigms) of how to view giftedness, how it develops, how to identify and measure it, and how to manage it, are becoming so dominant. But this is not a complaint about what Ruf actually said -- my guess is that in her PhD etc. she has thrown in a million disclaimers or caveats -- but the way her research is being used. It is creepy -- we need more diverse sources of research and a range of views to be cited. Contrary to the impression that you get from the most popularly cited bits of Ruf's Levels of Giftedness descriptions and profiles, intellectual giftedness isn't consistent from birth; most children even don't develop perfectly linearly. They develop in spurts and plateaus. There is such a thing as a late developer, which Ruf's most commonly cited descriptions seem to preclude. Ruf is a big believer in the utility of IQ or similar tests (she has even developed her own assessment test for intelligence), but IQ tests are only rough snapshots of intellect, and only truly applicable in the moment they are taken -- that caveat isn't coming through most of the time when people use her categories to describe children's intellect.
Moreover, assigning levels of giftedness -- while it may help parents in assessing their own children's short-term needs -- it is bound to become both a point of competition between parents, and a restrictive label. That's not healthy for anybody involved.
I just wish that people -- especially parents -- were advised to take Ruf's classifications and results with a bit of skepticism. It's just one set of results, just one way of looking at precocious intellect among children. It's far from definitive. It doesn't necessarily say anything about your child's abilities or potential.