Birth order, stimulating environment, and maternal factors in developmental outcomes: A longitudinal Mexican study.

This study longitudinally examined the interplay between birth-order and well-known risk factors in impoverished environments such as inadequate environmental stimulation, low maternal education, and young maternal age in children from birth to 36 months. In the developmental motor domain, the effect of the stimulating environment over time, favored first-borns. In the adaptive domain, maternal education privileged first-born boys.