Susan Rodriguez, formerly Susan Chung, stood in front of a small classroom in Medellín, Colombia, pointing to words written on a whiteboard while twelve students ranging from teenagers to elderly professionals repeated after her; the afternoon sun streamed through the open windows, and the sounds of the bustling city filtered in, creating a backdrop of honking horns and distant music that had become comfortingly familiar over the past three months.

"Again," Susan said in Spanish, then ...