Fannie Fern Andrews, a Boston educator and reformer, started the American School Peace League (ASPL) in 1908 in order to educate schoolchildren in the principles of what she called "world citizenship." Through its curriculum, "A Course in Citizenship," the ASPL taught students about cooperation, tolerance, and the peaceful settlement of disputes. At the same time, however, they were preparing white, native-born US children to lead the new world and to judge others' capacity for membership in it--their fitness for world citizenship--according to "civilized," white American standards. I argue that while Andrews and the ASPL professed a desire for internationalism, theirs was very much a US-dominated internationalism. "A Course in Citizenship" calibrated the standards of progress and civilization by which children were to measure not only themselves but others around the world. Education for peace was also education for the new American empire.