We evaluated emergent stimulus-stimulus relations after two different training procedures. Participants were five typically developing preschool children and three individuals with Down Syndrome. Experiment 1 used two-comparison matching to sample (MTS) to establish AB and BC relations. Experiment 2 used two-comparison and blank-comparison MTS, each on 50% of training trials to establish AB and BC relations. In both experiments, tests for emergent relations (AC, CA) were conducted to assess equivalence class formation. In Experiment 2 subsequently, class expansion was assessed after CD training. All participants showed positive equivalence test outcomes. Seven showed class expansion. After class formation tests in both studies, probe tests were conducted for and relations in baseline relations. Initial results were somewhat variable, but became more consistent after class expansion.
