“teachers provide the most obvious example of the ambiguity of class identification in the United States, for while income provided the single clearest indicator of class standing, it did not tell the whole story.” (XXIV, Introduction)
Nell Irvin Painter writing about the early 1900s in Standing at Armageddon: The United States, 1877-1919. (Published 1987, Penguin Books)
“Class in the United States has been more and less than a matter of struggle or relations of production, by which social scientists generally define classes.”
I presume that struggle of production or relations of production refers to the means of production l. That is, the struggles or relations of land and labor and capital.
Most of all, I delight in the clarity of the “most obvious ambiguity.”