This sub-series includes correspondence related to the Congress of Mothers, an early iteration of the Parent Teacher Association. The Washington State chapter of the Congress of Mothers was founded by Abby Williams Hill in 1905 and she served as its first president until 1911. The organization focused on education, health, and safety issues related to children and youth. In addition to this correspondence, other items related to the Congress of Mothers can be found in the News Clippings, Printed Materials, and Ephemera series.