Drawing on a rich lode of social history--letters, evangelical tracts, the prescriptions of educators and medical authorities--Kett (History, Univ. of Virginia) traces the rise of ""adolescence"" as a ""distinct, critical and incapacitating"" stage of life. One might add, a volatile and dangerous one, during which young men and especially young women, were best kept institutionally segregated in high schools and adult-sponsored civic and church groups. Delving back into the 18th and early 19th centuries, Kett presents copious evidence that a far greater ""age heterogeneity"" was the norm in both schooling and the workaday world. The 18th century knew only ""youths"" under which rubric both 10- and 25-year-olds were subsumed; only ""infancy"" was a period of total dependency. Kett shows evidence that ""leaving home"" was often seasonal and accomplished in stages, and that growing up was not synonymous (as it later became) with the ""gradual removal of restraints."" A pronounced shift occurred in the antebellum period, as middle-class moralists began to shower the country with ""conduct-of-life books"" which exhorted ""character building"" as preparation for the nascent success ethic. Evangelical zeal and fear of the urban, ethnically diverse lower orders propelled the reformers who fastened on ""puberty"" as a crucial period of development. Despite the spread of Boy Scouts and YMCAs, Kett believes their efforts to control the young were never totally successful; urban fire brigades, political organizations, et al., tended to span age cohorts and work against isolating adolescents into passive, innocuous organizations designed to preserve innocence. If he has a central thesis it is that ""the historical relationship between generations and between social classes within generations is more like a snake dance than a yawning chasm."" Exploratory and panoramic--for academics and others with a serious interest.