Changes in Intelligence Over a Quarter of a Century

The purpose of the investigation is to study changes in intelligence among Swedish 13 year‐olds during a 25‐year period. The results show that the average of spatial and reasoning intelligence has successively risen. Concerning verbal intelligence, there is a clear increase during the 1960's. After this period the growth has been more irregular. No changes in the differences between social groups were observed. On the other hand, this was the case between boys and girls. In verbal ability, there were only small differences between the sexes in 1961. However, in 1985 the girls were clearly ahead of the boys. In spatial and reasoning ability, the boys were superior in the early 1960's. Twenty‐five years later this difference had almost disappeared.