The recent secular trend in height of primary school children was estimated using data from schools participating in the National Study of Health and Growth in 1972, 1979 and 1986. About 50% of the trends from 1972 to 1979 for English and Scottish boys and girls were accounted for by changes in family size, with some contribution from increases in parental height and from birthweight, but almost none from changes in social class distribution. Estimates for 1979-1986 showed that the trend towards increased height in five-to eleven-year-old children has now ceased.