Since the study was about male children, I’ll answer for hubby. He is the youngest of three boys and by far, the smartest.
My sister is older than me by five years and is, well, severely lacking in the common sense and educational ambition that I have.
I don’t think so. I don’t know my little brother’s IQ, but it has to be within 5-10 points of mine. I wouldn’t be surprised if it were even closer than that. I was always the better student, but he’s very bright. He realizes it too 
I couldn’t guess at my dad’s family since I’ve only met 2 of his 4 older half-siblings. In my mom’s family it’s definitely not true. My second-born mother’s a dysfunctional genius, my aunt not so much; though she’s probably still somewhat above average. My poor uncle, the third in the series, is probably normal at best.
I’m not sure.
According to Mother, my brother got a higher IQ score than I did, and he’s 18 months younger than me.
My father was the second of three kids, and he was the first member of the family to go to college. (That doesn’t make him smarter. It just appears more intellegent.)
Yes, going by I.Q. Mine is twelve points higher than my younger sister’s. (Not that I place much value in IQ anyway. My sister is the more successful of the two of us.)
My brother is younger than me and vastly smarter.
The oldest in my family is my sister, who’s eight years older than the youngest–me.
She’s not smarter than me. That is, if you define smarts as scholarship, high test scores, academic degrees, and knowledge of useless trivia.
But if you define intelligence as social skills and athleticism, she’s got me beat.
Well I can’t speak for my generation as I’m an only child. But I can only say my mom has a big sister who married some total ahole in New Mexico annd gave up her art career (noth that i was was that great to begin with) whereas the second born (mom) got her PhD, the third born is an important exeutive at Nation Geographic. The fourth one is kind of feckless,but hey it’s a crapshoot.
I’m the eldest of six kids and have a Ph.D. in literature, so I’m pretty bright (I like to think).
However, my brother who is the mid-kid is finishing his doctoral degree in a hard science, so I think he wins.
Yes. And while I haven’t read the news today (oh boy) I think it’s because the eldest does a certain amount of teaching, and also because the eldest works harder to stay ahead of the next sibling.
Not in my family. My oldest sister is fairly intelligent, the next two are about average, and the youngest two are the smartest. (I think I’m a wee bit smarter than #4, but that’s arguable, I suppose. Her college GPA was slightly higher, and my IQ is somewhat higher, and I have more college degrees than she does. Competitive? No, why do you ask? )
Gypsy, youngest of 5
I think my family ends up being pretty even, top to bottom. None of us have any problem holding our own.
My eldest brother is the most socially accomplished, for certain.
My skills lie in a completely different range than the rest of my family. They’re all math/engineering people, and I’m a poet.
Nope. My baby brother is more intelligent, as well as better read and educated.
Step-kid set #1 – the middle child is the the smartest of the 3.
Step kid set #2 – the baby of the family is the brightest of the 5.
Of my inlaws, oh *hell * yes. Hubby’s the oldest of 5, including his half wit half-sisters.
The oldest is smarter in traditional ways – school, career, interests, all that.
The youngest is smarter in the sense that you would rather be with him if you were dropped behind enemy lines with no equipment other than a stapler, a deck of cards, and a jar of peanut butter.
In Mr. Del’s family, the oldest has the most practical smarts, the middle is the most book smart, and the youngest is crafty to beat the band.
Most definitely. But my 5 younger siblings aren’t stupid.
Among my siblings, the even-numbers win out - 2 and 4 are considered smarter than 1 and 3, and all are definitely smarter than 3.
I’m an even. My sister (the other even) is able to specialize and focus more than I, but there’s a lot she doesn’t know and couldn’t care less to know: for example, I’m sure what she “knows” about astronomy could make for some good fodder on that BBQ pit thread currently going.
I’m the oldest.
My younger brother is also a member here.
So… I take the Fifth. 
Not true in my home. Oldest (girl) has the looks. Middle (me, male) has the brains. Baby #1 (male) has the personality. Baby #2 (11 yrs younger than rest of us) has…well, it’s too early to tell, but I don’t think it’s brains.
I am MUCH smarter than my sister (I’m the oldest), and she unfortunately suffered in school because of it.
In my children, though, it doesn’t seem to ring true. Geek Child #1 (son, age 14) brings home C and D grades (a lot of which is due to lack of effort… AAARRRGGHH!!! and I can’t seem to get through to him how he’s screwing up his life). Geek Child #2 (daugher, 12) is the one who brings home the straight A’s and seems to have a real passion for learning. Geek Child #3 is still at the stage where his report card is checks and pluses, so it’s hard to say where he really stands.
I’m 3 of 4 with sisters older and a brother younger and I’ve been smarter all my life, to the lasting irritation of my older sisters. When my father had an emergency triple bypass 2 years ago and I was discussing his labs with the RN, my middle sister said " You may be the smart one, but I’m the pretty one."
“Not anymore.” I said, not bothering to look up.
My oldest is smarter than her brother.