flippant. Parents wish to know about the comparative effectiveness of different types of schools, and social scientists have an obligation to try to furnish the best possible answer.
We have sought to answer this question by conducting research in New Zealand. U.S. readers may question the relevance of a study of school contexts in New Zealand for youths in the United States. Indeed, the two nations' school systems differ in important ways. Still, because the selection effects in New Zealand schools are considerably less pronounced than those in the United States, the New Zealand project offered a unique opportunity to capitalize on a "natural" experiment. Of course, our efforts to reduce "intake" differences between different types of schools -- whether through conducting research in New Zealand or through the introduction of statistical controls -- are not enough. It is possible that we have failed to render the two different types of schools equivalent, even with adjustments for the most relevant intake differences, and our conclusions must be interpreted accordingly.
The conclusions that we can draw are sobering, however, because they suggest no clear-cut solution to questions about the comparative effects of schools. Debates about the comparative effectiveness of schools are often reduced to dichotomous alternatives. With regard to the gender organization of schools, the question is asked: Which are better, coed or single-sex schools? Our research suggests that these debates obscure both the complexities of adolescent development, as well as the challenges that confront students, parents, and teachers.
It appears that the effects of different school environments on adolescent development depend on individual differences in pubertal timing. The gender organization of schools may influence pathways through adolescence, but this influence varies according to the timing of physical maturation. Males in the classroom are more disruptive for young women than for little girls (never mind that the "young women" and the "little girls" were born in the same year).
These findings serve to remind that the impact of biological events on behavioral development is controlled by the social context of development. These findings also suggest that uniform interventions in the gender organization of schools are useless because they will have different effects on different persons at different times. Social policies and educational reforms cannot be mandated on the basis of such conditional effects. However, conditional effects can be used to alert parents to the potential consequences that their school choice will have for their children.
This work was supported by U.S. Public Health Service Grants from the Personality and Social Processes Research branch (MH-49414 to A. Caspi), the Antisocial and Violent Behavior Branch (MH-45070 to T. E. Moffitt) of