Once compulsory systems of state-run schools were established, they became increasingly standardized, both in content and in method. For the sake of efficiency, children were divided into separate classrooms by age and passed along, from grade to grade, like products on an assembly line. The task of each teacher was to add bits of officially approved knowledge to the product, in accordance with a preplanned schedule, and then to test that product before passing it on to the next station.
Peter Gray, Free to Learn: Why Unleashing the Instinct to Play Will Make Our Children Happier, More Self-Reliant, and Better Students for Life
education, science