Everything I was taught, and many people still believe, about women in physics is wrong. Okay, there's my strong sweeping statement for the blog using the "everything you thought you knew" meme.
That being said, I get into this discussion often enough for a blog post. Women are underrepresented in physics classes and related careers, and they have been for a long time. It seems to be a common belief that it's due to a difference in abilities. I just don't see that. I never have. I have encountered plenty of women that believe it, too, and that's an easily self-fulfilling prophecy.
What I have seen is a difference in interest, not ability. At both Leonardtown and Northern, honors classes were 50-50, because anyone college bound generally took it. For all my classes, I posted the top 5 academic scorers. This practice caused a few opinions that didn't seem to come up when track teams posted the fastest times in each event, but that's a discussion for another blog post. From my lists, updated every half quarter, I saw a 50-50 split again. Sometimes classes were full of successful male students, sometimes all the top scorers were female, but the average came out eventually. That didn't translate to equal AP enrollment. When I took over Northern's program, there was 1 female in a class of 15. It took me years to achieve equal enrollment, and I only did it once (male enrollment increased steadily, too). Mostly, I was able to get it to around 30-40%. The difference between my male students and female students was simply that I didn't have to recruit the boys. My strongest guys always signed up anyway. My strongest girls needed convincing. It was the girls that told me physics is a boys' thing. It was the girls that often assigned that to different abilities. When I pointed out all the girls in my current top 5, other girls tended to dismiss each one as an anomaly. Some of my best female students dismissed or ignored their own abilities. Lauren told me in the first month that she's just not good at physics. She was wrong. She's an engineer now. I'm always going to brag about that. Kara hadn't missed a single point all year (well, after she realized the top 5 were posted and she had no intention of being 2nd), and she tried to convince me she wasn't that good. I still lost her to AP Bio, but at least it wasn't because she didn't know physics was a serious option. I wanted the best students for my program, just like every teacher does. My female students needed more convincing than my male students, but the quality of work was just as high.
Another claim I've encountered many times is that women learn differently than men. I encountered it a lot at IUP, where there were 2 female faculty and 1 grad student in all my 4 years in the physics department. I encountered it slightly less among my US colleagues, and I encounter it noticeably more in the UK. I just don't buy it. "Women are like this, and men are like that" makes for great stand up comedy, but poor educational policy. First of all, half the world population sharing a learning style just sounds far fetched. Secondly, learning is not that easy to describe and predict. My anecdote on this is the fact that I was told repeatedly in college that teaching physics to women necessitates dumbing down the math (though I'm pretty sure the female faculty were not the ones telling me this). Sure enough, I avoided mathematical explanations to my girls for a while. I remember it was Jenny that made me notice the error of this. I failed repeatedly to explain instantaneous velocity until I mentioned the slope of the tangent. "Oh, it's just the derivative" was her response. From that moment on, I found exactly what I should have thought. Mathematical explanations work for some people more than others. No gender trends in my experience there.
My main job is usually finding the right example or comparison to make a concept click in my students' heads. I have explained gas pressure using mosh pits, radiation using wasps and horses, light using paleontology, and weightlessness using the Demon Drop. I use whatever works. In that way, there may be examples that work more often for women than men. I do find long haired people having more life experience with static electricity, for one. I do remember Celena and Natalie telling me to "use more girly examples." Not all girls think alike, but I took their meaning and varied it up more. They noticed and appreciated it. If someone's into video games, I use that. If they're into horses, I use that. If they're into theater, I use that. In my experience, people learn best by connecting new material to stuff they already know. My job is finding that connection, and it's different for everyone.
I'm working in a girls school for the first time in my life, so I can't say what all the advantages and disadvantages are, but I am noticing something positive for physics. I don't see girls dismissing their physics abilities or describing the subject as stuff for boys. Every subject is 100% female, so they seem to take whatever they like most and are best at. That is how it should be.
Try not to assume how successful or not you will be before you try, and try not to assume how successful or not someone else will be before he/she tries. And if you find success, try not to explain it away as a fluke.