What is needed to judge school effectiveness is a means by which schools can be assessed as "cultures" that create sets of relationships, norms of behaviors, and values and obligations that lead to the development of healthy and productive adults. The Hope Study was originally designed to evaluate whether the educational setting would produce more positive student outcomes than the traditional model of a secondary school. The basic proposition of the model grew out of the theory of adolescent development known as "stage/environment fit," which hypothesizes three core, overarching needs of adolescents: autonomy, belongingness, and competence. According to this theory, a mismatch between these developmental needs of adolescents and the educational environment can result in such negative outcomes as disengagement, dropping out, or behavioral problems. However, a better match between the needs of adolescents and the educational environment should result in higher levels of motivation, engagement, and achievement. In addition, placing students in a more developmentally appropriate environment should have a positive effect on student psychological health. To assess an educational environment, the authors measure the degree to which the school context supports the students' core developmental needs of autonomy, belongingness, and competence. In addition to measuring student perceptions of the environment in terms of autonomy, belongingness, and competence, they also gathered data on how students respond to the environment in terms of engagement and psychological health. In this article, the authors present convincing evidence that focusing on these needs is not at odds with No Child Left Behind's focus on raising student achievement. (Contains 16 endnotes.)