The study was designed to investigate the learning processes in discrimination shift learning, in terms of developmental views of "logical manipulation by classification." Tasks comparing sizes of intradimensional value-classes and comparing sizes of interdimensional value-classes were devised in order to measure subjects' levels of logical manipulation. Two groups of Japanese subjects, normal children and children with mental retardation, were each divided into two groups by the scores on the interdimensional task. The two higher groups consisted of children in Jean Piaget's concrete operational stage; the two lower groups were in Piaget's intuitive thinking stage. Results were as follows: (1) in reversal shift learning, there was no difference between higher groups and lower groups; (2) in nonreversal shift learning, the higher group of normal children met the task criterion in fewer trials than the lower group, but there were no differences between the higher and lower groups of children with mental retardation; (3) the lower groups of the normal children and of the children with mental retardation attained reversal shift learning more easily than nonreversal shift learning; and (4) the higher group of normal children exhibited no difference between the reversal and nonreversal shift learning processes. (JDD)