Maria Kraus-Boelte was widely recognized as the foremost authority on the Froebel Kindergarten (Froebel's widow called her his "spiritual daughter"). The two-volume set, The Kindergarten Guide, which she wrote with her husband John Kraus, was the de facto Froebel Kindergarten training manual in the late 19th century. Highly regarded and still relevant today, these profusely illustrated volumes provide a solid introduction to the use of the Froebel materials. 486 pages (5 by 8 inch) spiralbound paperback reprint of the 1882 edition by The Froebel Foundation USA (2001).