Mental retardation, mental age, and learning rate.

Zigler's hypothesis that mental age (MA) and not IQ determines the rate of learning is examined in the light of empirical evidence comparing the learning rates of normal and retarded children and young adults matched for MA. The results show that learning rate is a function of IQ as well as of MA. In general, children of average IQ learned serial and paired-associate lists significantly faster than retarded young adults with IQs between 60 and 60 but with approximately the same MA as the children. An interaction between IQ, learning rate, and socioeconomic status is also noted.