I'll try to respond to a couple of things.
One, I think, is that in Sierra Leone, for example, which is somewhat unique with its post-conflict scenario, there are much fewer female teachers in the classrooms. The girls don't have those mentors, those role models to look up to. One of the things that the TGEP is doing is paying for scholarships for young women to go to teachers' college to increase the number of women who are in teaching and in the classroom.
Another thing is that girls are starting later than boys. One of the things we know for sure is that if they don't catch up, if they don't advance, they will drop out. That's in part because of the pressure from their families. If they're not achieving, really the families would just as soon quite often have them at home doing domestic work or working in the market. There are also the pressures of early marriage. Girls in Sierra Leone are getting married at 13, 14 or 15 years of age, and that's often an economic reality. In some countries, the ages are, in fact, quite a bit younger where you first start seeing early marriage.
I think there is also still a gender imbalance in the sense of the quality of the materials. I've spoken about literacy and the importance of getting kids to be reading and writing, because that's the gate that opens up the rest of the learning to them. If they aren't able to read and write, they can't then progress in science, math, history or whatever the other subjects might be.
Often the learning materials, if available, put forward stereotypes of girls, stereotypes that they should really be looking to other, more domestic realities for themselves.
I think that gap is one that's based on a number of things: on the quality of teaching, on the quality of the resources available, on the fact that they're starting late, on the fact that there is often more pressure for them to leave in the first place, and on the fact that there is a lack of role models.
I am probably not doing a great job of expressing them, but these are the main points that are impacting young girls.