In order to examine the nature of dimensional processing in children, kindergarten and third grade children were asked to make similarity judgments for unidimensional sets of stimuli differing in color (hue), size, and shape, respectively. Age differences were generally confined to the color set. The judgments of the older children in their age group than were the younger children's. The frequency of good-fitting scaling solutions was also higher for the older children. The processing of color in a relational manner thus seems to develop more slowly than relational processing of size or shape. Results from any task which depends on or is facilitated by relational processing could be altered by the dimensions used. The methods developed in the paper also provide an alternate method of studying seriation .