The influence of birth weight and socioeconomic position on cognitive development: Does the early home and learning environment modify their effects?

OBJECTIVE: To establish whether effects of birth weight and socioeconomic position on cognition are explained or modified by home or learning environments. STUDY
DESIGN: Prospective birth cohort (n = 13,980) with math tests at 7, 11, and 16 years of age and qualifications by 33 years of age.
RESULTS: For 1 kg increase in birth weight, 7-year math Z score increased 0.23 (0.19 adjusted for parental interest in child's progress) and adult qualifications increased 0.22 (on a 5-point scale). Maternal reading benefited math less among lower than higher birth weights (p < .05). The birth weight effect remained unchanged 7 to 16 years of age. For each increment in social class (4 categories; IV&V to I&II), 7-year math increased 0.19 (0.12 adjusted for parental interest). Benefits of mother's reading and father's interest were greatest in classes IV&V (interaction p < .05). The difference in Z scores between classes I&II to IV&V was 0.57 at 7 years; 1.12 at 16 years of age. Estimates were little affected by home and school factors. Adult qualifications increased 0.40 per unit social class (0.33 adjusted for parental interest). Maternal interest reduced the chances of those from unskilled manual origins gaining few qualifications (p < .05). Similarly, interactions were seen for maternal reading and paternal interest.
CONCLUSION: Influences in the home partly underlie associations between social background and cognition, but they do little to explain a birth weight/cognition association.