Minnesota Symposia on Child Psychology: Volume 4 was first published in 1970.This is the fourth volume in a series which is based on papers from the annual Minnesota Symposia on Child Psychology, sponsored by the Institute of Child Development at the University of Minnesota. The basis for this book is the material from the 1969 symposium. For each symposium a number of outstanding child psychologists are invited to give papers dealing with their respective programs of research.This volume contains six papers by eight contributors: “The Effects of Early Life Experiences on Developmental Processes and Susceptibility to Disease in Animals” by Robert Ader, University of Rochester Medical Center; “The Antecedents and Adult Correlates of Academic and Intellectual Achievement Effort” by Virginia C. Crandall and Esther S. Battle, Fels Research Institute; “The Role of Peer-Group Experience in Moral Development” by Edward C. Devereux, Jr., Cornell University; “The Development of Motor Skills and Social Relationships among Primates through Play” by Phyllis Jay Dolhinow and Naomi Bishop, University of California, Berkeley; “Systems of Perceptual and Perceptual-Motor Development” by Herbert L. Pick, Jr., University of Minnesota; and “Mental Elaboration and Proficient Learning” by William D. Rohwer, Jr., University of California, Berkeley.