Published online by Cambridge University Press: 31 July 2008
Eleven-year-old boys and their parents from southern Ontario, Canada, were used to examine relations among sibling constellation variables, social status indicators and a set of parent-sibling interaction variables which were highly predictive of mental ability performance. A two-term equation including father's occupation and either sibsize or the inverse of sibsize parsimoniously accounted for as much significant variance in the parent-sibling variables as complex many-termed equations. Within each socioeconomic group the amount of parent-sibling interaction decreased as the family size increased. It was also found that in high social status groups the amount of interaction in large families was greater than in small families from lower social status groups. By using refined environmental measures the study provides an increased understanding of the relations between social status, sibling constellation variables, family environment and cognitive performance.