The major purpose of this investigation was to study the structure, attributes , and supplemental aspects of equivalence classifying of words and pictures made by sixth graders, freshmen college students and junior and senior college students . A particular point of interest was whether or not increasing or decreasing the size of the groups results in different types of equivalence classifying. Other minor goals were to determine the effects of direction of grouping, type of stimuli, and class level on unique reasons produced and recall of stimuli. The results of the study support the thesis that there is a cognitive developmental progression which supports the works of Piaget, Bruner, Vinacke and others. Children, compared to college levels, use a less efficient grouping structure, lower level simple association and concrete and perceptual grouping attributes, lower quality responses, and more specific reasons for grouping. College levels, compared to six grade, use more representational grouping attributes, have higher quality responses, and have a more general level of specificity. In addition, decreasing grouping structure results in a high level of cognitive performance in all aspects of grouping. There were no main effect differences between the words and pictures. However, there were significant interaction effects involving directions, stimuli, and class levels. There were more stimuli recalled and unique reasons produced by the college students. More pictures than words were recalled by all groups. One implication of the results is that decreasing the size of groupings apparently results in a higher level of cognitive functioning. One reason ventured for this result is that decreasing group size results in more divergent thinking and allows the individual to contemplate more possibilities for his groupings. Increasing group size is related to convergent thinking in which the subject is hindered by a previous set. Another implication is that there is a cognitive development a l progression which results in an increasingly more sophisticated ability to deal with the complex stimuli of the environment. Also, there is some evidence that different grade levels handle pictures differently than they do words. More study is needed to clarify the role of different forms of stimuli in classifying. From this study it is clear that there are no main effect differences between words and pictures. However, there certainly appear to be some interaction effects, and these need further clarification.