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Three experiments explored reaction times and the emergence of consistent responding during tests for equivalence following prerequisite conditional discrimination training for the establishment of three 3-member classes. Using a simultaneous testing protocol following linear series training, Experiment 1 investigated differential reaction times to baseline and to test trials, and the consistency of emergent test performances. Only 1 of 1 0 subjects responded in accord with stimulus equivalence, and 2 subjects responded in accord with other consistent patterns. Reaction times to test trials were longer than to baseline trials, and there was a tendency for lower reaction times to be associated with consistent responding during testing, whether or not the consistent responding was in accord with equivalence. Experiment 2 investigated reaction times and the emergence of consistent responding during training as a function of repeated training and testing. One subject from the previous experiment participated in eight replications with the stimulus materials from Experiment 1 and two replications with a second set of materials. Neither of these produced stimulus equivalence, even after baseline and symmetry test performances were nearly perfect. However, with both sets of materials, reaction times were gradually reduced as responding became consistent with a different pattern during "equivalence" testing. To examine whether the longer reaction times initially during testing are directly relevant to the emergence of consistent responding and, under favorable conditions, stimulus equivalence, the opportunity to respond to comparison stimuli was restricted to 2 s in Experiment 3. The results showed that with the reaction time constriction, none of the subjects responded in accord with equivalence under otherwise favorable conditions, that is, following one-to-many training. A problem-solving interpretation of equivalence formation is suggested.