I think sex ed in my schools started at about age 10 and was repeated yearly until age 17, as far as mandatory stuff goes. There were some optional electives in high school (like Advanced Health) that included some sex ed as well.
Obviously none of them were UK schools, though. All three were in the US, and my youngest sister (who is just 5 years younger than me) didn't get as much sex ed as I did in high school due to a group parents who complained to the school board (oh noes, the kids will have THE SEX if you tell them it exists!).
We never put condoms on prosthetic penises, though. My health teacher was forbidden (by the local school board or the state, I can't remember which) to show us a real condom. We could see pictures, and we watched our share of explicit videos, but we couldn't see an actual condom.
I don't remember a lot of kids laughing, aside from during the videos we were shown at age 10. In high school I don't actually think there was giggling, though. I wouldn't really call it a clinical experience, either. Aside from the explicit videos, we also watched stuff like
And the Band Played On and had guest speakers (people who were HIV positive, teen mothers, etc).
Oh, at my middle school they
did try the abstinence-only thing on us once. Not very effectively, I might add. They had a bunch of kids from high school come to talk to us about their decision to wait to have sex until marriage (uh-huh, sure), and one of the school counselors showed us a balloon. She'd blown up the balloon a few days before, and almost all the air had leaked out. This was supposed to demonstrate that we should wait for marriage because obviously condoms aren't effective and will let diseases and sperm slip through.

Yeah. Right. I pondered raising my hand and asking her if she thought maybe, just maaaybe the air had leaked out through the knot she'd tied, rather than the actual latex of the balloon...but I was even more horrifyingly shy back then. I was also 13 and thought that I actually would wait until marriage (

), and their little presentation didn't even have
me convinced.
It's funny, because the high school I went to was in a
much more conservative town. Abstinence was mentioned as an option, but the focus of the sex ed classes was always on how you should protect yourself if you did decide to have sex. It's probably considerably different now, though, if the way it was headed when my sister went there is any indication.
Edit: CM, I would have almost definitely done the stupid thing at age 14, but my nervous stomach saved me. I threw up on the guy's floor instead and then went home. Go team Cand.