2 groups of Ss ( n = 50) were tested on one of two practice conditions on a large muscle motor task to determine the effects of distribution of practice on true score variance (individual differences) and intra-individual variability. Under distributed practice conditions (30 sec. work-30 sec. rest) the true score variance decreased 49% while under massed conditions the decrease amounted to 13%. The corresponding decreases in intra-individual variance were 37% and 11%, respectively. Only the decrease in true score variance under the distributed condition was significant.