With over 122 million copies sold from 1838 to 1920, the McGuffey Eclectic Readers taught more Americans to read than any other textbook. Initial publication coincided with a unique period in United States history as the West was settled, newly arrived immigrants assimilated, and the common school movement gained momentum. At this time, the nation was at a critical point of forming a distinct identity. These phenomena created a demand for textbooks that would not only meet the practical need for curriculum in developing schools but would also extend prevailing American values both to children new to the frontier and to those new to the nation. The McGuffey Readers proved to be to the 19th century what the New England Primer was to 18th-century, except to a much greater degree.
Samuel J. Smith. "McGuffey Readers" Encyclopedia of Educational Reform and Dissent (2010).