In the 1840s, German educator Friedrich Froebel founded the Kindergarten movement, a program of preschool education that encouraged children to learn through self-directed play with specialized balls, blocks, sticks, papers, pencils, and modeling clay. The series of 20 devices and play materials-called gifts and occupations-were designed and sequenced to teach children about the forms and relationships found in nature and to develop their creative faculties and problem-solving abilities. Notable American architects and artists like Frank Lloyd Wright had recalled playing with Froebel's gifts as children and credit what they learned from the experiences with influencing their career paths and their distinctive designs. Some makers of educationally materials, especially game manufacturer Milton Bradley, produced Froebel materials and other kindergarten items for the growing number of kindergarten classrooms that appeared throughout the nation in the later years of the 19th century.