Parents are right to be stricter with older kids.

• Position: YOUR LIFE

If you think your parents let your younger siblings get away with everything, you probably are right. A study from researchers at Johns Hopkins University, Baltimore, Md., and the University of Maryland, College Park, concludes that parents punish older children more harshly--and they are wise to do so.

"Games Parents and Adolescents Play" finds evidence that parents are more likely to withdraw financial support from older siblings who either drop out of high school or--in the case of girls--get pregnant, than their younger brothers and sisters who wind up in the same situations. Further, the paper presents a mathematical model that supports such unequal treatment of children because more severe discipline of older kids deters younger siblings from engaging in the activities for which they know their older siblings were penalized.

The researchers began by constructing a model of parent-teacher interactions using the logic and mathematical tools of game theory, which assumes "-" that mothers and fathers want their adolescent children to avoid long-term negative consequences that can result from risk-taking behaviors, such as drinking, drug use, sexual activity, and dropping out of school. Teenagers, on the other hand, are assumed to value the short-term thrills of risk-taking behavior while also wanting to avoid punishment. The authors posit in the model that parents need a...