This paper illuminates how concepts of rationality developed by Diesing in l962 are reflected in parents' childrearing decisions. After examining technical (TR), economic (ER), social (SR), legal (LR), and political (PR) rationalities or decision-making styles, consideration is given to integrative effects and the influence of parents' friends and relatives upon childrearing decisions. TR is construed in terms of the parenting goals of efficiency, maximization, and achievement; ER in terms of scarcity of time, energy, and resources, and the maximization of utility; SR in terms of confirming, supporting, and reinforcing behaviors leading to consistency and integration of roles; LR in terms of family rules and behavioral norms; and PR in terms of negotiation, discourse or bargaining. The childrearing decisions examined are based on observations of the home environment of a two-parent family with an 11-month-old daughter. Discussion focuses on how each type of rationality is involved on an unconscious or conscious level as parents make choices about those experiences of their child which involve a significant amount of adult attention, response and direction. (RH)