By the beginning of the twentieth century, the diversity and range within the urban middle class were striking. Indeed, it makes sense to replace the idea of a single “middle class” with a confederation of “middle classes” whose members engaged in occupations requiring mental, rather than physical, skill.

Below the wealthy top tier, the much larger, much less wealthy, and increasingly diversified middle class included moderately successful industrialists and merchants as well as professionals in law, business, and medicine. As industry and technology expanded in the nineteenth century, a growing demand developed for experts with specialized knowledge, and advanced education soared in importance among the middle classes. Engineering, for example, emerged from the world of skilled labor as a full-fledged profession with considerable prestige. Architects, chemists, accountants, and surveyors, to name only a few, first achieved professional standing in this period. They established criteria for advanced training and certification and banded together in organizations to promote and defend their interests.

Management of large public and private institutions also emerged as a kind of profession as governments provided more services and as very large corporations such as railroads managed ever-larger numbers of human and physical resources. Government officials and many private executives had specialized knowledge and the capacity to earn a good living. And they shared most of the values of the business-owning entrepreneurs and the older professionals.

Industrialization expanded and diversified the lower middle class. The number of independent, property-owning shopkeepers and small business people grew, and so did the number of white-collar employees — a mixed group of traveling salesmen, bookkeepers, store managers, and clerks who staffed the offices and branch stores of large corporations. White-collar employees owned little property and often earned no more than better-paid skilled or semiskilled workers. Yet white-collar workers were fiercely committed to the middle-class ideal of upward social mobility. The tie, the suit, the soft, clean hands that accompanied low-level retail and managerial work became important status symbols that set this group above those who earned a living through manual labor.

Relatively well educated but without complex technical skills, many white-collar occupational groups strove to achieve professional standing and higher social status. Elementary school teachers largely succeeded in this effort. From being miserably paid part-time workers in the early nineteenth century, teachers rode the wave of mass education to respectable middle-class status and income. Nurses also rose from the lower ranks of unskilled labor to precarious middle-class standing. Dentistry was taken out of the hands of working-class barbers and placed in the hands of highly trained (and middle-class) professionals.