Some argue that you can only effect change by altering girls' social environments. A study in Jerusalem conducted by Neumark-Sztainer, Butler, and Palti (1995; as cited in Binford & Fulkerson, 2000) sought to do that. The sample consisted of 341 10th-grade girls (mean age = 15.3) in three all-girl high schools. All classes in one school were assigned to receive intervention; all classes in another were assigned to the control group; and all classes in the third school were randomly assigned to intervention or control. Girls in the intervention group received 10 hour-long classes on eating disorders, nutrition, body image, and avoiding social pressures to be thin. In addition, the investigators altered the school environments by involving teachers and providing them with training in eating disorder prevention-teachers facilitated informal conversations among students regarding eating and weight concerns. Girls were encouraged to take an active role in creating healthier norms in the school, not just to avoid pressures and harmful messages. Results were seen 6 months and 2 years later: girls in the intervention group had improved nutritional knowledge and more regular patterns of meals, and the intervention also prevented the onset of binge eating and excessive dieting. Thus, across these several studies, it appears that simply teaching adolescent girls how and why to avoid developing eating disorders raises their awareness but does not alter their behavior. In order to alter behavior, school-based prevention programs must seek to alter girls' social environments in addition to teaching them lessons.