Table 3.

Associations Between Duration of Breastfeeding and Measures of Cognitive Ability, Teacher Ratings of School Performance, Standardized Tests of Achievement, and High School Success After Adjustment for Covariates

MeasureDuration of BreastfeedingPSignificant Covariates*
Not Breastfed<4 Months4–7 Months≥8 Months
Mean cognitive ability scores
 WISC–R total IQ, 8 years98.7099.65100.59101.54<.0051–3, 5, 8, 9
  9 years98.9699.78100.60101.42<.011–3, 5, 8, 9
Mean teacher ratings of achievement
 Reading, 8 years2.952.993.023.06>.151, 2, 5, 7–9
  12 years2.932.983.033.08<.101, 2, 4, 7–9
 Mathematics, 8 years2.892.973.063.14<.0051–3, 5, 7–9
  12 years2.872.973.073.17<.0011, 2, 5, 7–9
Mean standardized achievement test scores
 Reading comprehension, 10 years98.8699.76100.66101.56<.0052–4, 7
  12 years98.9199.75100.59101.43<.012–4, 7, 9
 Mathematics, 11 years99.0699.77100.49101.21<.051–3, 5, 7–9
 Scholastic ability, 13 years99.1399.81100.50101.18<.052, 3, 5, 7–9
High School Attainment
 Mean number of School Certificate passes3.053.223.403.57<.0051–9
 Leaving school without qualifications (%)22.219.216.414.0<.051–4, 6–8
  • * Covariates: 1 indicates maternal age; 2, maternal education; 3, family socioeconomic status; 4, averaged standard of living (0–5 years); 5, averaged family income (0–5 years); 6, maternal smoking during pregnancy; 7, gender; 8, birth order; 9, birth weight.