A classical IQ model of the stages of cognitive development

Based on the construct of classical IQ (mental age/chronological age), a model of the proportions of the population at various stages of cognitive development as a function of age is proposed. The model, which accounts well for empirical data for the age range 13 through 17 years, is shown to compare favorably with other theoretical models. The success of the model provides further evidence of the salience of the construct of general cognitive capacity in differential psychology.