Simple reaction time (RT) was divided into cognitive and motor time to more closely determine the developmental changes in cognitive processing time. In previous studies the assumption has been that motor time did not interact with age, thus RT represented changes in cognitive time. Those studies found age differences and one reported unexplained gender differences. Motor (MT) and cognitive time (PMT) were determined using e.m.g. to fractionate RT. Thirty-seven children in 5 age groups (3.5, 5.5, 8.5, 10.5 and 12.5 years) completed a minimum of 10 practice and 10 test trials by lifting the index finger from a depressed button. Simultaneous auditory and visual signals were presented after variable fore-periods that were initiated with a verbal warning. The average time from the practice trials was used as a reinforcer during the test trials by providing computer generated claps and whistles each time the RT was faster than the average. The age main effect for RT was significant in a 2 by 5 ANOV (F(4,42)=24.35, p=.0001). Scheffe follow-up tests found the youngest children different from all other groups who were not different from each other. The 3.5 age group had a standard deviation of 3 to 10 times larger than the other groups. When the youngest age group was deleted from the analysis, significant age differences were noted for non-adjacent groups (e.g., 8.5 and 12.5 were different from each other). The gender main effect was not significant. A 2 by 5 mulitvariate analysis (gender by age for MT and PMT) resulted in a significant age main effect (F(8,72)=7.07, p=.0001). The gender main effect was not significant. Univariate follow-up tests indicated age group differences for both PMT and MT. Again the 3.5 group was different from all other groups for PMT and MT. With the youngest group dropped from the analysis only PMT was significant, and the non-adjacent groups were statistically different from each other. Three findings from this study are: motor time differs between pre-school age children and school age children, RT, MT and PMT do not differ between the genders as previously reported, and the great variability in young children as compared to older children may mask differences among older groups. Reaction time decreases during childhood. During the preschool years the motor time makes a greater contribution to RT than in older children. Thus, RT is not as representative of decision making in younger children.