Those who believe that truth lies in decimal points will find Kessner's study of social mobility in turn-of-the-century New York a statistical treat. Selecting Russian Jews and Italians, both of whom came to the US in droves during the period, Kessner turns to census reports and city directories to find out how they fared. With a curt dismissal of such squishy stuff as ""diaries, letters, newspapers . . .folk songs,"" he groups the immigrants into a five-step class scale based on occupation. Jacob Riis would marvel to learn that Lower East Side Jewish pushcart peddlers make it all the way up to grade II, ""Low White Collar."" (Italian rag pickers languish in grade I, the bottom of the heap.) On to the conclusions. By Kessner's evidence, ""America's promise was fulfilled in the dynamic immigrant city""--far more than Stephen Thernstrom and other historians working in this field have realized. People upgraded their vocational status over time--the Jews much more so than the Italians for a variety of culturally defined reasons. Unlike the Italian peasants who often worked only to take money back to Italy, the Jews came to stay; they had entrepreneurial savvy and they valued education. Overall, the golden door to the promised land was no myth, though ""sober gradual mobility"" was more the rule than rags-to-riches. Astonishing it's not.