In 2014, after a brief orientation course and a few fingerprinting sessions, Nicholson Baker became an on-call substitute teacher in a Maine public school district. Nearly every morning, he awoke to the dispatcher's five-forty a.m. phone call and headed to a nearby school. When he got there, he did his best to follow lesson plans and help his students get something done. In Baker's hands, the inner life of the classroom is examined anew -- mundane...