Before there were schools, there were apprenticeships. Young people learned a trade from a journeyman, and once these young people attained a certain level of mastery they were able to make a living in that trade. Apprenticeships still exist, of course, but the majority of young people in the U.S. receive a formal education by attending traditional schools.
Apprenticeships, as the primary means of educating young people, were fairly inefficient when compared with the model of schooling we use today. Working professionals had to invest quite a lot of time teaching and supervising a small number of apprentices (although they did benefit from the free labor provided by the apprentices). With the more efficient public school model, a relatively small number of teachers, support staff and administrators can educate nearly every child in the country, while the rest of us are able to focus on our jobs. In addition, the K-12 system is designed in such a way that by the time students complete high school they have a much broader base of knowledge than apprentices who only learned one trade, theoretically enabling high school graduates to choose any career path.
Despite their inefficiency, however, apprenticeships did provide one thing that schools are often less successful in fostering: deep relationships between young people and adults. Apprentices and masters spent so much time together that they got to know each other very well. It’s not hard to imagine that even after apprentices left their masters, the relationships probably continued. Because of the number of students they see every year, teachers are unlikely to forge lasting relationships with more than a few children.