Because there is a need to measure performance of pupils with complex concepts, the Slide Sorting Task was developed to measure performance on complex concepts of freedom, non-freedom, justice, non-justice. The development of this instrument was presented along with the results of item analyses with several groups of subjects ranging from age seven through adults. The utility of the instrument was shown as a means of differentiating instructional procedures similar to those in regular classrooms. The instrument was shown to differentiate performances of abstract and concrete thinkers and to produce improved performances as a function of increases in age level. (Author/DEP)