The Development of Children’s Concepts of Causal Relations was first published in 1937. Minnesota Archive Editions uses digital technology to make long-unavailable books once again accessible, and are published unaltered from the original University of Minnesota Press editions.This is a report of group tests administered to 732 school children between 8 and 16 years of age, in grades 3 to 8. The children were asked to explain 11 scientific demonstrations, such as putting out a candle with a glass jar, and 12 commonly observed natural phenomena, such as snow and thunder.Quantified scores herein are analyzed in relationship to age, sex, intelligence, school grade, and socio-economic status. The results give insight into children’s logical processes and the development of thinking.