Three studies of five seventh-grade students (ages 12-14) with emotional disturbances were conducted to determine whether a stimulus class would emerge as a result of one conditional discrimination training using direct instruction (implemented with a constant time delay) augmented with instructive feedback. The students were taught to identify fractions and their equivalents in lowest form and multiplied by factors. Each of the three experiments are described. The results indicate that, after modifications in the placement of the lowest form of the fraction, the students were able to form a stimulus class. This was accomplished with minimal number of trials and training time, near errorless learning, and in a classroom setting with group instruction. Factors that affected the results are discussed, including students' history or experience with the procedure. Further research is urged to merge the phenomenon of stimulus equivalence and direct classroom instruction. Charts illustrating each student's acquisition percentage are included. (Contains 24 references.) (CR)