I have no idea.
My parents gave me an “Teenagers questions about sex” book when I was about 13, and I remember thinking, “I know all this.” That was just the basics, though. Our school did not teach sex education at all (this was the 60s, when sex ed was not routinely taught in public schools.
The rest was experimentation. I was a quick learner, and I went by one guiding rule: I’m probably normal. Also, I had no interest in sex until I was about 17 (though I’ve made up for lost time).
(Please excuse the expletives)
Actual conversation between myself and friend when we were 10.
Him: You know what “fuck” means, right?
Me: Yeah.
Him: Well, what does it mean?
Me: It’s a swear word. It’s like “damn”.
Him: No, it means when a guy puts his dic in a girls pussy.
Me: Dude, your sick in the head.
Him: No, it’s true, And that’s how a girl gets pregnant.
Me: You are so full of shit.
Him: Am not.
Me: You are too. If that was true it would mean our parents have done that and there’s no way in a million years that they have done that.
Him: Yeah, I guess your right.
Then six months later between seeing some sex on cable tv at a friends and hearing about where babies came from in school it hit me “Holy crap, he was right.”
I also remember discovering masturbation on my own without ever hearing about it. I thought I had just discovered the greatest discovery in the world. “My God” I thought, “I wonder if anyone else knows about this? I have just made the greatest discovery in the history of mankind!”
When I was in fifth grade, I remember that a whole group of girls from another classroom came into our classroom, while the boys in our classroom went to the other girls’ classroom. We (the girls) watched a film about menstruation. One of the boys told me that they watched a film about male puberty, but didn’t go into too many details.
Around the same time, my mother brought home a book about how babies are made, showed it to my sister (a year younger than me) and me, told us to read it, and let her know if we had any questions. I remember that it was a pretty detailed book about how babies are made, complete with pictures. However, there was no mention of erections, and the only picture of actual copulation was missionary position (and a cartoon drawing, rather than a photo). I had seen flacid penii before (two little brothers, and glimpses of my father using the toilet when I accidentally walked in on him when I was very young), so my poor, undeveloped brain just led me to the assumption that gravity was necessary to get the penis into the vagina. To me, it all made perfect sense, so I never bothered to ask my mother any questions. I do remember her telling me explicitely on more than one occasion that masturbation was not a Bad Thing, but I had no clue what the word masturbation meant, and didn’t really see much reason to look it up.
In eighth grade, we had a sex education unit in our science class. By today’s standards, it was very liberal, with a model of an erect penis that the teacher used to demonstrate the use of a condom. (This was in the mid-70’s.) That was where I found out about erections. That was also around the time that I found out what an orgasm was. I had learned a couple of years earlier that if I sat on my heel in a chair in a particular way, and rocked back and forth a little, it felt VERY good.
Most of the rest was just experimentation. I had a few serious boyfriends as I moved through college–most with as little experience as I had–and pretty much had everything worked out by the time I met the man I decided to marry.
I now have a 13yo daughter. Remembering how “in the dark” my mother had left me, I made a point of sitting down and talking to her about EVERYTHING when she was 10 and starting to develop breasts. I swear I told her everything I could without going into personal details that would embarass her. However, a couple of weeks ago, she told me that she didn’t remember anything about that talk, and that she thought she had learned more from her friends than she ever had from me. :smack:
I learned about sex in all the standard ways:
Formal sex education begun in my school was I was in the
fourth grade. By the sixth grade we were told the dirty
facts. But I couldn’t understand how a penis can stay hard
to enter a vagina much less way anyone would want too.
They told us we would understand later. My brothers’ porno
magazines we much more helpful in the former. The books
and stories in Playboy were useless in this.
A few months later I found myself enjoying showers,
especially very hot showers. I’d spend hours in there
bathroom scrubbing myself down. I’d scrubbed everywhere,
even between toes and then finish it off with a body
lotion-RoseMilk.
Eventually, I got bored and started doing naughty things:
I discovered that if I kept rubbing my penis, ot would
stay hard.
A tire needle my brother left on the counter could be
inserted into my urethra and feel good. Later I found an
enema kit, complete with all the attachments, in the
bottom of the towel shelf. You can guess where I inserted
this. One of the attachments was for douching-about five
inches long. That went in too. And then I thought, hmm,
that hairbrush has a tapered round handle… Lastly, I
used a screwdriver, also left by my brother.
But the penultimate naughty thing I did had to play with
my GI Joe doll- the John Glenn series. Everyday, he would
ride my rocket until my mother tokd me to get out!!
But then one day, I broke GI Joe !! A metal staple holding
together elastic bands attached to his head, arms, and
legs rusted thru and broke into six pieces. No longer
would Joe go on his joyride.
I turned to just rubbing my penis, just like we did in
school to polish the hand carry flag poles in the JPO’s.
Because my brothers rightly claimly, I was using too much
hot water in showers, I switched to just using the tub and
filling it to a few inches. I started using soap because
it starting to hurt a little because of the friction I was
generating.
But then one day, I broke my penis too!!! “Soap” began
pouring out of my penis!! And an ache I never felt before
caused my penis to pulse and jerk. I rinsed off quickly
and tried to squeezed out the “soap” that must have worked
itself into my penis. I swore to myself to never do that
again.
However, I found peeing was no problem, so I thought
myself no worse for wear. The next day, I decided to
continue, without using soap. I used only a dribbling
shower stream, but the friction still hurt, so I just
lathered myself only halfway up my penis and was careful
not to get any on the top. Soon that strange ache returned
and I realized that what I found myself shooting out what
wasn’t/couldn’t have been soap. Then it clicked in: this
was semen!! And this was an orgasm!! My first venture into sex has begun!! :eek: 
Parents told me absolutely nothing in childhood, and I remember that back when they still used to kiss and pinch each other, my sister and I would always make exaggerated barfing faces and noises if we saw them. After all, anything your parents enjoy doing has to be lame, right?
Later between about the ages of eight and ten, I gleaned from somewhere an understanding of the basic mechanics of vaginal intercourse. I resolved that I was never going to do anything so disgusting as long as I lived, and couldn’t imagine that anyone found it enjoyable. In the fifth grade, the girls and boys were separated to watch a movie about “growing up.” The girls’ movie mostly consisted of an explanation of menstruation. WTF? You mean I’m going to bleed from there? You have to be kidding me. We had to have a permission slip signed by our parents to watch the movie, but they didn’t ask me what I thought.
I viewed menstruation with trepidation. It didn’t help that the movie gave one the impression it could happen at any time and embarrass the holy hell out of one.
I never had much interest in sex itself until I actually started menstruating, which was not pleasant, though I hadn’t expected it to be. I began reading my mom’s romance novels at about age thirteen. I went through them at a rapid pace. The sexual descriptions were enthralling, and I had my first orgasms from reading these scenes. Somewhat later, it occurred to me that I could masturbate. But wait–girls don’t do that, right? Just boys. Who cares, I thought, it’s my body and I’ll do it anyway. This was my introduction to several happy years of masturbation. I discovered later that plenty of girls masturbated, which was a relief to me, because I’d thought I was some kind of freak for doing it as often as I did.
I had a few boyfriends during high school but remained a virgin and had very little other sexual experience. I was a mass of hormones but didn’t want to have sex with some silly teenage boy. I was also terrified of pregnancy. (I tend to be a bit of an alarmist, especially when I was younger, and the mere idea of contraceptive failure rates scared the bejeezus out of me.) I discovered that I was bisexual at about age fifteen and had a girlfriend, though it was a very secret relationship for both of us. I knew everything there was to know about sex with other girls (I thought) but didn’t pursue much with the opposite sex, though boyfriends tried to get me to have sex with them. I read a lot, as usual, and stored information for the time I thought I would need it.
I commenced an uneven program of practical experience with the opposite sex at about age twenty. Learning goes on to the present time, somewhat erratically.
I remember my parents explained how sperm and ova worked to me a short while before I had sex ed classes in school [we watched a couple of videos over the span of a few weeks in both fifth and sixth grade]. Very un-graphic, of course. They explained what a sperm looked like (an egg with a tail) and what it does when it gets to the ovum. Nothing about how it gets from one place to the other, but hey. 
I’m not sure how I finally figured out “Ah, THAT goes THERE.” I don’t think my parents said it, and I’m pretty sure the school wouldn’t have. Maybe it was just common sense, but I may be giving myself too much credit by assuming I have any. So there was some info from parents, some from schools (sex ed in 5th, 6th and 8th and 11th grade as part of health education was probably more than I needed). Doesn’t leave you that prepared for the real-world situation, though.