Robin Hammond photographed 80 nine-year-olds in eight countries around the world for National Geographic's January cover story. He photographed equal numbers of boys and girls, and also looked for other kinds of diversity: geographic, ethnic, socio-economic. He asked each child the same nine questions about how being a boy or a girl played out in their everyday lives.

"Nine-year-olds are old enough to articulate their lives, but [they're] not quite adolescents," Hammond says. "We thought this age was an interesting time to ask them about their feelings about their gender."

One of the children Robin photographed was Avery Jackson, from Kansas City. Avery spent the first four years of her life as a boy but has been living openly as a transgender