Temperament and intellectual development: a longitudinal study from infancy to four years.

Using three temperamentally different subgroups from a large birth cohort, the authors undertook a longitudinal study of the association between temperament measured in children at 4 and 8 months and IQ assessed at 4.7 years. The data suggested a strong effect of extreme temperament traits on IQ development in middle and upper socioeconomic classes and in families with superior functioning in terms of communication. The temperamentally difficult group unexpectedly displayed higher IQs, and the well-replicated effect of socioeconomic status on IQ development was observed mainly in this group. These data support the hypothesis that difficult infants activate special family resources, which stimulates intellectual development over the years.