From the article:
The unadjusted associations found that longer breastfeeding durations were associated with higher verbal and spatial cognitive scores at all ages up to ages 14 and 11, respectively. After taking the differences in socioeconomic position and maternal cognitive ability into account, children breastfed for longer scored higher in cognitive measures up to age 14, in comparison to children who were not breastfed. Longer breastfeeding durations were associated with mean cognitive scores 0.08 to 0.26 standard deviations higher than the mean cognitive score of those who never breastfed.