Peak velocities in height and mental performance. A longitudinal study of schoolchildren aged 10-14 years.

The relationship between spurts in height and in mental performance was studied by following a sample of Swedish urban schoolchildren from age 10 to 14 years. The children were grouped into early, average and late maturers with peak height velocity age (PHV age) as the criterion. A mental arithmetic test was administered once a year from grade 3 to 7 inclusive (10-14 years). Gain/year and level of performance were analysed both for a pure longitudinal sample (examined every year) and for mixed longitudinal samples. Early- and average-maturing girls had a maximum gain/year in performance about one year earlier than late-maturing girls. In boys, only early maturers seemed to have a peak in performance gain. Results from mixed longitudinal analysis indicated that gain/year curves were different for girls and boys. In level of performance, late-maturing girls were inferior to average and early maturers. No differences between maturity groups were found for boys. Girls were superior to boys in grade 5 (age 12) and grade 6 (age 13) in level of performance. Social background had a great impact on level of mental performance measured by this test. The relative influence of physical maturation and social background on level of mental performance was approximated as the ratio of the mean difference in test scores between early and late maturers to the mean difference between social group I + II and social group III. The ratio fluctuated over the grades 3 through 7; physical maturity seemed to have the greatest effect in grade 5 (age 12) for girls and in grade 7 (age 14) for boys.