In countries where not enough girls are going to school, NGOs and policymakers have tried everything: giving people money as an inducement, building more schools, trying to make sure kids are safer as they walk to class -- you name it.
In India's northeastern state of Bihar -- one of the country's poorest regions -- just 53 percent of women were literate, a rate 20 percentage points lower than that of its men. School is expensive for most and too far away for many, and by age 16, only about 45 percent of girls are still enrolled, compared with about 65 percent of boys.
"We found that the high school dropout rate soared when girls reached the ninth grade. This was primarily because there are fewer high schools and girls had to travel longer distances to get to school," said Anjani Kumar Singh, Bihar's principal secretary overseeing education.
Here's a chart showing how female school enrollment drops off, particularly for girls, as they get older:
So in 2006, the state's government tried a different, more vehicular solution: they gave all 9th-grade girls money to buy a bicycle in order to make the trek to class a little easier.