hi all,
I hear very often that siblings tend to be within 10 IQ points of each other. If IQ is heritable, and parents are quite different from one another IQ-wise, then this does not make sense to me. It would seem that its just as likely that 1 kid will take after 1 parent, and the other may take after the second parent, or a an aunt etc.

In my case, my oldest son is HG, esp in math (3 grades accelerated) and shows all the classic characteristics. My middle kid seems fairly normal development wise. He seems to struggle with a lot of learning but I have a hard time telling if this is just normal and I'm comparing to my oldest or if there is something there (he's 6 1/2 and just starting to read etc). I have a 20mo old as well and she seems more like my oldest (already knows all the letters) but I'm pretty sure with her I'm overthinking it.

I'm wondering what your experiences are and if you have a mix of gifted and non gifted kids or if they are all similar.

thanks!
Sabina

Hi Sabina,


If you are just looking for experiences, here is mine: after DD9 was tested last year, our tester told me that it was not uncommon for siblings to be in the same IQ range (but with different strengths). I looked into this myself, and found some sources that suggested the same thing - without LDs, siblings are often VERY close in IQ (http://www.giftedminds.com.au/attachments/Like_Minds.pdf). Low and behold, DS6 was recently tested and compared with his DYS sibling, he is within 1-3 points FSIQ/GAI (both of my DC have lower WM/PSI, than VCI/PRI, but no LDs).

Even though I'd known that it was possible, I still found it freakish that they were THAT similar.

My two are not genetically related but very close in IQ. I posted on a recent thread about how close they are with their scores...both were in the 140's for non-verbal (Perceptual Reasoning) with a lower verbal score (DD did better than DS with verbal ability, however). And both have weaknesses with processing speed. What are the odds of taking two random kids off the street and having both score in the 140's for non-verbal ability, with that being the highest score for both? Probably not very great. I think siblings tend to be close in IQ, but there are other things going on besides genetics which have influenced cognitive development. Both in terms of the strengths and the weaknesses.

I wouldn't call myself dumb, but my brother would probably have a much higher IQ score than me if we were tested. And our abilities are very different. I remember taking the PSAT and was in the national merit program, but it was because of my verbal score. My brother is a high energy physicist and excels most at math and non-verbal ability. The stuff he does is Greek to me (both literally and figuratively). So siblings can be very different. My brother is much brighter than anyone I can think of in the family--comparing him to my parents, grandparents, etc. So if it came from genetics, it's not obvious who had those genes.

I have one gifted & one non-gifted. My older DD is not gifted, she has LD's and is "above average" in intelligence. My DS has clearly been gifted since he was little, taught himself to read at 3, etc. Just had him tested and I don't have the full scores but it's clear he is at a lot more than 10 IQ points of each other.

Haven't had my kids tested, but I do know that there is a roughly 40-50 point range among my siblings.

My daughter consistently scores very high on ability and achievement tests; she is a DYS. My son had developmental delays that I initially didn't recognize because I only had my daughter for comparison. He no longer has delays and his teachers say he is very academically advanced, but even now he tests 30-40 points lower than her on IQ tests. It's possible he may have some exceptionalities affecting his scores, but there is clearly a big difference between them regardless.

Here is the an article I've seen commonly referenced.

http://www.gifteddevelopment.com/articles/what-we-have-learned-about-gifted-children

I would consider the sample rather small. They are saying 40 percent of the sample doesn't test within 10 points of each other.

I would also consider a younger sibling of a HG child may look different. My DD looked very different compared to her older brother. They have FSIQ scores 2 points apart. She is actually stronger than him in many areas, but he was so intense and she is so laid back. DD started reading at 5 compared to DS at 2 yrs old. At 7, she is the same level of reading he was at 7. It just didn't look like another PG kid when comparing her to him. My oldest DS isn't within 10 points of the younger siblings.

There is a huge range of giftedness and difference in personality. Mine are 15 points apart. Since the higher score is very high the lower score is still high HG range. However the younger is a perfectionist and has a low frustration threshold so he may in fact be closer to the older.