Genes contribute and the library was a constant in our lives. No preschool even though all the moms were pushing it and acted like if your child didn’t attend they were going to be behind for life. I had 4 kids who kept each other entertained and didn’t need the colds brought home from preschool. My 3rd child I could tell at age 3 that he was probably highly intelligent from the questions he asked me about religion. He did everything early and loved playing online chess with adults at age 6. I parked him in the kitchen and he played while I cooked.
Just had to jump in on this, because there are plenty of studies that show that children’s acquisition of language is totally not dependent on the style with which they were addressed by their mother or anyone else. (This is assuming that linguistic abuse—e.g., completely refusing to speak to the child, ever—doesn’t factor into the equation.) Vectoring claims that it’s the mother’s fault are problematic on a number of levels, but particularly when there’s good science saying it just isn’t so.
ETA: In fact, if the child was learning English and the mother was a non-native speaker of the language, children are exceptionally good—using mechanisms we’re not entirely certain of—at filtering out and completely ignoring non-native-speaker inputs, so she wouldn’t have been a factor here anyway.
Average for Cornell, perhaps, but let’s not be falsely modest. That still makes her one of the smartest people in the country, and the world, in terms of percentiles.
I just got off the phone with my D who flew in last night from Taipei after 10 weeks there with the Department of State and before she starts back at Stanford (grad school). Since we are all bragging, she fits in very well with the paradigms mentioned here. She was read to a lot, was reading herself at her 4th birthday party (the other kids refused to believe she was reading the cards herself), doing math well above her level at 6 (she had just turned that age when at a bookstore I gave the person a $20 for a $12.84 purchase and my D said immediately “you get $7.16 back”. You could have literally knocked me over with a feather), and of course was curious about everything that moved and much that didn’t. I would also say that we discussed many topics among ourselves (my wife and I) that a lot of people I think don’t in front of kids. Not that the topics were inappropriate, but that many, maybe most adults think it is weird somehow to talk about why something happens chemically or why this company merged with that company in front of very young children. We didn’t think it was strange, and if they (my son also) had questions I answered in terms basic enough for them to at least gain some understanding. FWIW, my D was a straight A student in high school with many AP’s, 2330 SAT, accepted to every school she applied including several USNWR top 10, attended Tulane on full tuition scholarship, graduated summa cum laude and Phi Beta Kappa, accepted to all the grad schools to which she applied including Harvard, Princeton, Berkeley and Columbia and as I said is attending Stanford, on full scholarship for a masters. Now that we have established her bona fides with regard to intelligence:
So in this phone call, it came up somehow about how so many of the kids at these elite schools suffer from the “Impostor Syndrome” and/or the “Duck Syndrome”. The former is, in short, that they somehow made a mistake in admissions and that they really don’t belong there with the people that really are smart, while the latter is the belief that everyone else is doing so well in their classes and in life without breaking a sweat while they are killing themselves to just keep up. The reality instead being that while people might put on a serene facade, they are also working very hard when no one else is looking, just like a duck seems to be doing nothing but is churning its feet furiously under the water.
At some point having a sharp mind still requires hard work if anything productive is to come of it. But to get back to the main topic, I haven’t read every post, but it seems like a somewhat overlooked point is the science of the brain. Or at least it is only implied in some of the answers, even if the poster didn’t know it.
While we still have a lot to learn, it seems clear that the type and number of connections made within our brains are constantly developing through adolescence, but most especially in the earliest years, say 0-7ish. That is why we are little sponges at first, then have to start memorizing more and more as we get older in order to learn something new. It is well known, for example, that it is much easier to learn foreign languages at a very young age, and if you do you always remember at least some of what you absorbed. Waiting until high school is a huge mistake by comparison, as you have to pretty much memorize everything. Now we know the brain adapts, and that if you stay with something long enough, or totally immerse yourself in it, different mechanisms will kick in. Similar to how after a head trauma the brain is sometimes capable of forming new pathways, albeit usually slowly.
So the point is that while there is no doubt a large genetic component, the frequent referral to having lots of books around, reading to them a lot, exposure to tons of other stimuli (music is a big one), all feed into what I describe above. The more this can be done for children at the earliest ages, the easier it is for them to learn everything thereafter, hence the more fun it is for them, and the “smarter” they are. If only it were easy to actually make it happen in real life for a greater number of children.
@dfbdfb Interesting. All I know is what they told me the doctors told them, and that he is now much improved. However, I said “mostly” because there were other issues present.
Is that why my wife looked at me with a puzzled look when I mentioned that people were asking me that? 
Re learning English with a non-English speaking parent: my sister learned language with two non-English speakers changing her diapers and an older brother who was learning English at the age of 7. Nobody spoke English fluently in her home for a few years. It didn’t keep her from being #1 at Law School. Fwiw, she’s got the gift of gab.
As @whatisyourquest and others have noted, this thread is unusual because it seems to validate the idea (controversial and often refuted loudly in popular culture) that genetics play a large role as a determinant of cognitive ability. The interesting thing is that this idea isn’t really that controversial in the scientific community; the consensus view is that the heritability of IQ is in the order of 0.75 in adults (75% of the variance among adults is do to genetic factors), which is quite high. Moreover, heritability measures are actually highest in adulthood, suggesting that genetic influences become more obvious as individuals mature. Beyond this, the 25% environmental effect includes essentially random in utero development effects – a large component that is unalterable by parenting and other aspects of “nurturing.”
@wis75 post #106
I agree that the word “gifted” is uncomfortable. I only use it because it means a similar thing to a wide variety of people. (Actually not exactly the same, because is it 95%ile or 97%ile and is it aptitude vs achievement?) Perhaps “academically gifted” would be better, since clearly there are areas like athletics where “gifted” people are not “gifted” more often than the general population.
Very true that the smartest kids don’t always have the best grades. My son was basically “kicked out” of a Montessori preschool for being too much of an “abstract thinker” (their words). He was terrible at lining up beads before writing the answer. Many others have more dramatic stories of the problems their bright kids have had finding teachers that understood them.
Regarding Down syndrome, I don’t know about the variation you see other than to know that big advances have been made in recent years for both medical treatments for the physical effects and educational therapy. The outcomes you see may differ depending on when the kids were born and their access to the most advanced treatments.
That’s because smart comes in every color.
I recently had a garage “free” sale - getting rid of a lot of the boys early stuff. One of the best things out there I thought were these laminated place mats in nearly perfect condition. One had multiplication tables on it, another the period table, another the planets and so on. They stayed out there all day until someone finally picked them up near the end of the day (all except the lonely periodic table of the elements. 
Sorry @fallenchemist ) Meanwhile every single piece of sports equipment left as quickly as I put it out - no matter the condition. Every ball, bat, racket, Frisbee … gone.
It made me think that brainiac stuff is still an acquired taste and a road less traveled. Noticing the gold in the ore and pointing it out to the kids early - priceless.
@patertrium We had the periodic table and solar system placemats. (memories…) Ours didn’t stay in nearly perfect condition.
In response to OP original question, my retort would be “book smart, or street smart?” Two different things totally!
In memory of Oliver Sacks who just passed away, music also plays a big role.
Also, when I was 13 or 14, I remember our family friend’s mother, pregnant with her third child, who smoked quite a bit during her pregnancy. I remember seeing her on her patio, chatting with my mom with the ashtray balancing on her belly. Fast forward 20 something years and this baby became a Rhodes Scholar. 
I think the thread has moved along nicely without any unnecessary PC charges, so please indulge me in this anecdote about choosing a life-mate. We live in a very affluent town. Most couples are well-matched educationally, and the SAHMs are well educated; I am among the few SAHDs, although I have more company than I did a decade ago. There are however some number of “trophy wives” where their educational achievements were apparently not a significant factor in their selection (to anticipate objections: there are very few trophy husbands and I have no difficulty appreciating that beautiful women can be smart – I married one). With a few notable exceptions, the trophy wives don’t compensate for their intellectual lack with a generosity of spirit or grace.
It usually works out for the children, as they seem to average their parents’ traits, but every now and then my wife and I look at each other and say: “oh oh, Dad’s looks and Mom’s smarts.”
Absolutely #1, GENETICS- both my kids are ‘smart’.
2 Inherent natural curiosity (4.0+ kid has it, 3.6 kid does not)
3 LOVE of Reading (4.0+ kid has it, 3.6 kid does not)
4 personality traits like being organized and 'getting stuff done' mentality helps tip the scales on high achievement and effort (4.0+ kid very organized and very driven, 3.6 kid is not very organized or focused).
Don’t know about birth order? Maybe we would have forced the younger child (“3.6”) to read more (even though the desire was not there -at all) if that child was the older child… Maybe not.
I look at my kids, and I’m not sure. I’m sure genetics plays a role (both of us hold PhDs, though the first one was born before I completed mine, and all four before my wife completed hers), but that doesn’t explain the ways that our children show intelligence. Our oldest has classic “book smarts” and is probably destined for a life in the sciences, and our third has been laser-focused on something medical since she was four. That all makes sense—my wife’s doctorate is in engineering and mine is in the quantitative social sciences or humanities (depending on what mood I’m in that day), so sure, science and mathiness and related stuff fits.
But that doesn’t explain child two, whose brilliance shows up in the applied fine arts (and who’s way more of a driven individual than any of the rest of us, which is actually a better predictor of lifetime success than innate intelligence, and I would argue it’s a type of intelligence, too). Then there’s our youngest, who scores on intelligence tests way above what any of her sisters did at equivalent ages, but is clearly directing herself in a literature-major sort of direction, which is nowhere close to anything of her parents’ or even grandparents’ leanings.
So, to sum up, I’d say that my answer to the OP’s question is, in full: Go figure.
Most preemies will do fine that lack problems except for immaturity- some do have problems, especially severely premature ones. The boundaries of survival keep being pushed back but problems can occur. Those who do not have extra problems just need time to catch up.
Re preschool- that was the best daycare option, then kept him there when I quit working. the “Montessori Method” isn’t always followed. Fortunately for us son had an art major teacher who allowed creativity. She told me how son and a girl made a castle or some such instead of the expected tower and staircase (increasing sizes- boring).
btw- ALL teens and early twenties kids think they are so much smarter than their parents. Waiting for my kid to age out of it.
@TiggyB62 All forms of smart welcome. Contrarian and examples ad absurdum welcome too.
38 "random acts of scorn and derision"
Well played @Ohiodad51.
@wis75 As a preemie, maturity most often has to do with the way the child was raised as opposed to the physical age (unless we’re talking about peers who are two years older or more), IMO.
Probably the reason so many of us are citing genetics is that many of us have multiple kids for whom we have provided comparable levels of nurture, yet the kids have uneven levels of achievement.
Watching the courthouse news coverage of Amal Clooney defending the Al Jazeera reporters sentenced to prison in Egypt, makes me wonder what George & Amal chat about over the breakfast table.
While I would say that would strain the definition of intelligence to the point of making communication on the topic difficult, I completely agree with your point. The trait of being driven, not taking no for an answer, and seeing things through until you get what you want can often lead to great success, even if the person would otherwise be judged to be of average intelligence. Which I am not saying is the case for your child, obviously, just in general. Smarts plus great drive is no doubt an even more formidable combination.