The larger cause of failure is almost unmentionable: shrunken student motivation. Students, after all, have to do the work. If the students aren’t motivated, even capable teachers may fail. Motivation comes from many sources: curiosity and ambition; parental expectations; the desire to get into a “good” college; inspiring or intimidating teachers; peer pressure. The unstated assumption of much school “reform” is that if students aren’t motivated, it’s mainly the fault of schools and teachers. The reality is that, as high schools have become more inclusive (in 1950, 40 percent of 17-year-olds had dropped out) and adolescent culture has strengthened, the authority of teachers and schools has eroded. That applies more to high schools than to elementary schools, which helps explain why early achievement gains evaporate.