This study explored the hypothesis that Japanese children perform significantly better on simultaneous processing than on sequential processing. The Kaufman Assessment Battery for Children (K-ABC) served as the criterion of the two types of mental processing. Regression equations to predict Sequential and Simultaneous processing from McCarthy performance were derived from three validity studies of the K-ABC in which 123 American children were tested on both the McCarthy Scales and the K-ABC, and were applied to Lynn's analysis of Japanese McCarthy standardization data. Results of these analyses supported the hypothesis of a Japanese high Simultaneous-low Sequential profile, relative to American children, across virtually the entire 2.5 to 8.5 year age range. Cultural differences and brain functioning (left-right hemispheres) of Japanese versus American children are discussed. (Author)