But how will you know when educational opportunities are equal? If you subscribe to the idea that male IQ scores are more variable, then you will expect to see males over-represented at the extremes. If you don't subscribe to that idea, then you might expect more equal numbers. If you don't even know what to expect, then you can't discern a bias.
You have to look carefully at the opportunities, rather than at the statistical outcomes. (This is essential anyway, because even if, e.g. you think that there's a statistical tendency for boys to be overrepresented in the PG population, you *still* want to be sure not to miss the PG girl.)
Generally this may be complex, e.g., an opportunity may be theoretically equally open to both genders but in practice one may be more dissuaded by e.g. material that appeals to stereotypes (e.g. if you set maths questions about cars and trains that very young girls have learned to think of as boy things, you tend to put the girls off maths too).
Sometimes it's blatant though. Example from my own childhood: I was at an all-girls school, and very into maths. However, I was never entered for a maths competition (well, not until the one in my final year that took place when I was ill) although later I found out that many had existed and that comparable boys schools used to enter the boys for them en masse. And then people wonder why the winners of these competitions are disproportionately male... (I know, the whole story isn't as simple as that, but that kind of thing is part of it.)
