Background The benefits of exclusive breastfeeding (EBF) for infant health and survival are well documented. However, its impact on educational outcomes has been contested and poorly researched in Africa. It has been hypothesised that positive associations reported in high-income countries can be attributed to residual confounding by socioeconomic status (SES) because EBF strongly correlates with SES in these settings. Our study investigated whether EBF duration in infancy is associated with educational attainment and age-for-grade trajectories at school-age in rural Malawi.

Methods Longitudinal data on 1021 children born to women in the Karonga Demographic Surveillance site in Malawi were analysed. Breastfeeding data was collected in the first three months after birth and again at age one. The school grade of each child was recorded each year from age six, when they started school, until age 13. We calculated age-for-grade based on whether a child was on, over, or under the expected age for a grade. Generalised estimating equations estimated the average effect of EBF on age-for-grade. Latent class growth modelling identified age-for-grade trajectories, and multinomial logistic regression examined their associations with EBF. Maternal-child characteristics and SES were controlled. Stata 17 was used for statistical analysis.

Results Only 20.2% of the mothers had at least a secondary education, and slightly more than half (51.9%) of the children were male. Overall, 35.9% of the children were exclusively breastfed for six months. Over-age for grade steadily increased from 9.6% at age eight to 41.9% at thirteen. There was some evidence that EBF for six months was associated with lower odds of over-age for grade than EBF for less than three months (aOR=0.82, 95%CI=0.64–1.06). In subgroup analyses, children exclusively breastfed for six months in infancy were less likely to be over-age for grades between ages six to nine (aOR=0.64, 95%CI=0.43–0.94). Latent class growth analysis identified four distinct age-for-grade trajectories: (1) falling behind from early grades, (2) falling behind from middle grades, (3) falling behind from terminal grades, and (4) consistently on time for grades. There was some evidence that EBF reduced the odds of falling behind in the early school grades (aOR=0.66, 95%CI=0.41–1.08) but not later.

Conclusion Our study adds to the growing evidence that EBF for six months has nutritional benefits beyond infant health and survival, supporting the WHO’s recommendation on EBF. It also casts doubt on the hypothesis that beneficial effects reported in high-income settings are due to confounding by socioeconomic status.