Which elementary textbooks created by William Holmes McGuffey became widely accepted in schools for moral instruction?

William Holmes McGuffey's "McGuffey Readers" became widely accepted in schools for moral instruction because they were specifically designed to teach reading while also instilling moral values and ethical principles. These readers included a variety of stories, poems, and lessons that emphasized hard work, honesty, and respect for authority, making them a cornerstone of education in the 19th century. The content was aligned with the educational reform movements of the time, which sought to harmonize moral education with literacy. Consequently, McGuffey Readers played a significant role in shaping the character of American youth, reflecting the social values and norms of the period. This focus on moral education set them apart from other literary collections or texts that did not have the same educational goal.