The emergence of untrained relations resulting from stimulus equivalence enhances the significance of equivalence$-$based instruction $($EBI$)$ to learning. Key outcomes that add to the effectiveness of EBI include: $1)$ formation of equivalence classes resulting from testing and probing; $2)q,$ emergence $($ie$.,$ equivalence performance is frequently strengthened with repeated testing, $3)$ class $q,($i$.$e$.,$ new stimuli joining the class following training of relation with one member of the class$)$; $4)$ class $q,($i$.$e$.,$ combination of elasses following training of relation between one member of each class$)$; and $5)$ transfer of $q,($i$.$e$.,$ all members of the class having the same effect on behavior following training with one member of the class.