Chana Joffe-Walt spent six months reporting on the rise in people on disability. She spends time in Hale County, Alabama, talking to the only general practitioner in town, the main person who okays so many of the county's residents for disability. In addition to giving each patient a medical exam, the doctor also asks this question: what grade did you finish? Chana explains why that one question is so central to the whole story. (22 minutes)