This study was undertaken to determine whether neo-Piagetian theory might provide a functional interpretation of children's motor development, particularly linear positioning. In addition, intra-age and inter-age comparisons for both high- and low-mental-processing children were made. Pascual-Leone's Figural Intersection Test was used to select 15 high- and 15 low-mental-processing children from three public elementary schools. A linear-positioning test served as the criterion-referenced test and was defined as a multi-scheme task involving the repositioning of a pointer at the mid-position between any two of the three, four, or five completed movements along an arc of 225 degrees. Data were compared for six- and eight-year-olds on a three-scheme task, and eight- and ten-year-olds on a four-scheme task. Results indicated support for an age-related linear increase in mental processing across three dependent measures. This development appeared to be a maturational phenomenon occuring without the benefit of practice. The results also appeared to affirm that high mental processors of one age level would perform as well as or better than low mental processors of the next higher age level. It was noticed that the lower level of motor task performance than might be predicted by neo-Piagetian theory may well be due to the different focus of traditional (cognitive) developmental tasks and the present (motor task) study. The findings indicate that a child's mental space might be an important determinant of success or failure of those motor acts that require the activation and integration of considerable motor information. (MJB)