Selected electromyographic parameters underlying static postural control in 4, 6, and 8 year old normally and slowly developing children during performance of selected arm movements were studied. Developmental delays in balance control were assessed by the Cashin Test of Motor Development (1974) and/or the Williams Gross Motor Coordination Test Battery (1973). Twenty-four normally developing and six motorically awkward children performed three different static balance tasks, in three different conditions, while eight different muscle groups were monitored electromyographically. Normally developing children displayed little or no difference in the amount of muscular activity involved in postural control with or without a superimposed weighted arm movement. Slowly developing children exhibited higher levels of muscular activity in maintaining postural control when weighted arm movements were superimposed than when they were not. The average level of muscular activity observed in static postural task performance decreased with age for normally developing children, while there was no consistent relationship between age and level of muscular activity for slowly developing children. The implications of these findings are discussed in relationship to working with slowly developing children in motor control. (Author/JD)