McGuffey's Readers were among the first textbooks in the United States designed to be increasingly challenging with each volume. They used word repetition in the text as a learning tool, developing reading skills by challenging students using the books. Sounding-out, enunciation, and accents were emphasized. Colonial-era texts had offered dull lists of 20 to 100 new words per page for memorization. In contrast, McGuffey used new vocabulary words in the context of real literature, gradually introducing new words and carefully repeating the old.