This classic work on child psychology examines the mental development and behavior of children with intellectual disabilities. It covers topics such as sensory and motor development, language acquisition, intelligence testing, and educational methodologies. It provides valuable insights into the challenges faced by mentally deficient children, and highlights the importance of early intervention and specialized education. This work has been selected by scholars as being culturally important, and is part of the knowledge base of civilization as we know it. This work is in the "public domain in the United States of America, and possibly other nations. Within the United States, you may freely copy and distribute this work, as no entity (individual or corporate) has a copyright on the body of the work. Scholars believe, and we concur, that this work is important enough to be preserved, reproduced, and made generally available to the public. We appreciate your support of the preservation process, and thank you for being an important part of keeping this knowledge alive and relevant.