Toddlers from low-income families have below normal mental, motor, and behavior scores on the revised Bayley Scales

This study examined scores on the original and revised Bayley Scales of Infant Development (BSID-II) for 87 infants and toddlers from low-income families. Infants' scores were consistent with scores from the normative sample. In contrast, toddlers obtained mental, motor, and behavioral scores that were lower than scores from the normative sample. Mental, motor, and behavioral scores from the BSID-II were correlated for toddlers, but not for infants, suggesting that the interrelationship between behavior and development increases with age. These findings are consistent with longitudinal studies demonstrating a decline in developmental performance among toddlers from low-income families. They demonstrate that the vulnerability of toddlers can not be explained by outdated test norms. The findings may be partially explained by canalization theory in which early development is guided by species-specific self-righting processes that protect infants from all but the most devastating environmental influences or by a lack of enriching caregiving practices for toddlers in low-income families. With the restandardization of the BSID-II, more toddlers will qualify for early intervention. Recommendations are provided for prevention programs to reduce the vulnerability demonstrated among low-income toddlers.