There is a strong correlation between the educational level of a mother & how many children she will have. Studies have conclusively substantiated that women w/college & advanced degrees tend to have fewer children while women w/the least amount of education tend to have a large number of children.
Highly educated women know & realize the importance of family planning. They know that smaller families live better & there are more monies allotted to their children's cultural, educational, & intellectual development. They also see that small families are immensely beneficial to both parent & children in that such children have the chance to interact w/parents more & there is more individualized attention.
Less educated women thoughtlessly & mindlessly have children. They don't believe in family planning. They believe that somehow "things will work out." They have more atavistic premises regarding parenthood. These women are less interactive parents, oftentimes believing that children ought to raise themselves. They believe that interacting & giving individualized attention to children are spoiling them. It goes w/o saying that based upon the aforementioned premise, less educated women, on average, have large families. Other factors in less educated women having large families are religious beliefs as less educated women tend to be more religious than highly educated women who tend to be less religious.
Highly educated women view a woman's role beyond motherhood. They see themselves as multifaceted women & that influences their decision to have smaller families. Less educated women view a woman's role more traditionally. They believe that women's primary roles should be that of mothers. They further believe that motherhood is equivalent to true femininity. That influences them to have large families.