They worked, did farm chores, watched children and generally functioned in the real world. They got status and recognition for doing these things well, and they got shame and disapproval for doing them badly.
But once they were segregated by age in public schools, teens looked to their peers for status and recognition instead of to society at large.
December 26, 2012
"Putting kids together and sorting by age also created that dysfunctional creature, the 'teenager.'"
"Once, teen-agers weren’t so much a demographic as adults-in-training."