The choice mechanism in the economic theory of fertility as applied to developing countries is assumed, therefore, to exist primarily with regard to the additional (marginal) children who are considered as investments. In deciding whether or not to have additional children, parents are assumed to weigh private economic benefits against private costs, where the principal benefits are the expected income from child labor, usually on the farm, and eventual financial support for elderly parents. Balanced against these benefits are the two principal elements of cost: the opportunity cost of the mother’s time (the income she could earn if she were not at home caring for her children) and the cost of educating children the financial trade-off between having fewer “highquality” high-cost, educated children with high-income-earning potential ver
sus more “low-quality,” low-cost, uneducated children with much lower earning prospects.