I hate to sound like a snot, but I’d like to think I’m pretty smart or at least the smartest of my siblings- or at least liked learning the most. Older sister didn’t care about school, only scraped by with B’s because she had to. Younger sister works incredibly hard, that poor perfectionist, but gets high grades in regular to Honors level classes. I didn’t feel like I was trying all that hard to get my grades in AP/Honors classes. (Again, I feel gross writing all that, but for purpose of this thread!)
The biggest differentiator in between me and my siblings was definitely reading. My older sister read occasionally, and younger hated (hates present tense, too) reading more than anything else. I was reading all the time from the moment I could, anything I could- street signs, cereal boxes (I famously woke my mom up at 5 AM one weekend to ask her how to say “cholesterol” on the Cheerios box) to every book in the house. I (like many younger siblings) liked to do whatever my older sibling did, so when she was learning to read in kindergarten, I kind of learned with her. By the time I got to kindergarten, I was the most annoying kid in the class I’m sure because I was telling the teacher I already knew how to read this and spell this and blah blah blah (I SPECIFICALLY remember how painful it was to sit through other students “sounding it out”). By December, they had me tested in reading and I scored in the 99th percentile for first graders and the 96th percentile of second graders. My parents considered moving me to the second grade and just catching me up in the math, but were worried I’d be so young/only a grade below my older sister, 3 years older than me. So I skipped the remaining part of kindergarten and the first half of first grade over winter break. Unfortunately, at that point little me kind of knew I was “smart” and I’m sure I was annoying about it endlessly. Long story short: I think it all comes back to reading.
Fwiw, both my parents are smart (my mom in the math/science way, my dad in the reading/history way), but reading definitely was the differentiator.