Teaching ought to be a profession for hard-working altruists who want to improve children’s life prospects. But all too often school systems seem designed to attract mediocre timeservers. Many Mexican teachers have inherited their jobs; Brazilian ones earn less than other public servants, and retire much earlier. Each school-day a quarter of Indian teachers play truant. In New York it is so hard to sack teachers that even those accused of theft or assault may be parked away from pupils, doing “administrative tasks” on full pay, sometimes for years..