What about being able to procrastinate under pressure? 
English.
Being Spanish, I’d learned to read on my own, but learning to write was a bit more complex. While I might have learned it on my own given time, having someone handing out exercises helped.
Math.
Physical Sciences.
Typing.
Draftmanship, which I haven’t used in ages but helped reinforce my good grasp of geometry (very important for a chemist).
Problem-solving skills.
My 9th grade history teacher was absolutely exceptional. He never wanted us to learn piles of dates (like the other teacher who got three other sections); he wanted to get us interested in history and to learn to think independently. While 9th grade wasn’t compulsory back then, I say it’s close enough and you can’t change my mind (nyah nyah) 
He is an extreme example, but I had several previous teachers who wanted us to think and analyze. A notable case is a Religion teacher who was the sweetest old guy ever and who loved telling stories of the saints almost as much as he loved a student who talked back - so long as the student was being logical about things and not just a pain for pain’s case.
That some people don’t care about content half as much as they care about presentation. I wasn’t whore enough to put it into action until many years later, though.
That all teachers are idiots (5th grade).
That all adults are idiots (5th grade, a few hours later).
That some teachers aren’t idiots (6th grade); there may, therefore, also be exceptions among the general adult population.
pbbth, at one point the nuns wanted to send me to a special school in Madrid, claiming that I was a genius. My mother (who’s a teacher by degree but for some reason cough cough wasn’t able to get a job in the town where we’ve lived since I was four) explained that this would actually be unacceptable since, in order to be properly socialized, I needed to spend time with those who weren’t as fast as me.
The nuns didn’t even mention the possibility to move me one or two courses ahead (it’s not possible any more, but back then in theory a kid could be even three courses ahead of his age group so long as he kept the required grades; I’ve had classmates who were, respectively, one and two years ahead).
The kicker, finally?
Since my classmates would spend the two hours after class playing in the park in front of the school while I had to dash home,
and they’d also play there on the weekends while we went out of town,
proper socialization my ass. You don’t get socialized during lectures; you get socialized during breaks and off-class periods, and I only got half an hour of group play each day :smack:
To parrot the answer my dad always gave whenever I asked, “why do I have to learn that?”:
I learned how to learn (massaging the grey matter, as he said).
Social skills–I learned some there, more later in life. Being a geeky girl sucks in school.
Typing–wow, I’m glad I took that class.
Math–you use it every day, even if you don’t realize it. It’s usually done at an instinctive level.
Reading/writing–I learned to read for pleasure before school. I learned to read for comprehension during school. Structured writing is a whole 'nother ball of wax from just making sentences and paragraphs.
Public speaking–stood in front of my first audience to deliver a speech (brief to be sure) in 1st grade. Audiences have never held any terror for me.
What I didn’t learn: study habits, enough social skills, any sort of physical coordination (that came way later), confidence in myself as a woman, any number of practical things, world history–I was left to pick up or work out all the rest of that for myself.