What she never realized was that I've already implemented a 90% similar code twice in the last month in my spare time. Or that after she got off the school to hang out with her friends, I went to the library to do some reading, or write the next module of the awesome game I was developing.
What I'm trying to say is that in my experience the smarter ones is a lazy way of saying "the ones that had more interest and spent much more time on it already than you did". And of course, the argument isn't unique to girls and applies just as well to other guy friends. But in the end, in my experience it has always traced back to raw interest in the topic. So I've always said that girls are not different in any mystical raw Mathematical intelligence way, it's just that for some reason they tend to have less interest in these topics, on average. And why is that? Upbringing and early biases is my best guess - The mother who pulls away the rocket ship from a girls hands and puts in a Barbie is at fault. (But realistically, it is probably only one of the factors.) Worst of all, there is a positive feedback loop involved where if someone thinks they are not good at something, they will only become less and less interested.