Previous research has indicated that children who were breastfed scored higher on IQ tests and performed better in school but the reason behind this remained unclear.
Now a new study by sociologists pinpoints two parenting skills as the real source of this cognitive boost - responding to children's emotional cues and reading to children starting at 9 months of age.
"Breastfeeding mothers tend to do both of those things," said lead study author Ben Gibbs from Utah-based Brigham Young University.
"It's really the parenting that makes the difference," added Gibbs.
According to the analysis, improvements in sensitivity to emotional cues and time reading to children could yield 2-3 months' worth of brain development by age 4 (as measured by math and reading readiness assessments).
The scholars utilised a national data set that followed 7,500 mothers and their children from birth to five years of age.
Child development expert Sandra Jacobson of Wayne State University School of Medicine noted that children who were breastfed for 6 months or longer performed the best on reading assessments because they also "experienced the most optimal parenting practices".
The researchers found that reading to an infant every day as early as age 9 months and sensitivity to the child's cues during social interactions, rather than breastfeeding per se, were significant predictors of reading readiness at age 4 years.
The researchers also found that the most at-risk children are also the least likely to receive the optimal parenting in early childhood.