Professor Herbert invites Luster to spend the day at the school to show him new education methods and to help defuse his frustration at Dave being required to stay after school to pay for his part in damaging the cherry tree. He catches his interest by telling him that he has germs on his teeth. Luster replies by saying that he's lived 65 years and never seen a germ. Herbert tells him to stay and spend the day there.
After lunch, Pa scrapes tartar from his teeth and puts it on a slide. He looks into the microscope and is able to see the germs. Herbert shows him the other equipment that the school uses as well.
Though Luster is aggressive when he first speaks to Herbert, he quickly calms down and decides that he wants to stay for the class. The two men talk privately and have lunch together. Herbert proves himself and his new teaching methods to Luster. By the end of the day, Luster believes Herbert is a good man who deserves respect. He asks to help his son sweep so that the two of them can pay off the debt of the cherry tree. He tells Dave that Herbert is a good man and they're friends now.