Contents of this symposium comprises: Introduction (W. B. Dockrell); The Genetics of Intelligence (Sir C. Burt); Structuring Mental Acts (P. R. Merrifield); A "Piagetian" Test of Cognitive Development (R. D. Tuddenham); The British Intelligence Scale (R. W. Warburton); Intelligence (P. E. Vernon); Hierarchical Theories of Mental Ability…

Down Syndrome children (N=229), aged 1-83 months, from Australia, Canada, and Germany were tested using the Bayley Scales of Infant Development. Test performances on the Bayley's Mental and Motor scales were not dissimilar, leading to the conclusion that young Down Syndrome children from different countries with relatively comparable standards of…