2. The sample: The first cohort involved approximately 4000 students in 9 high schools in Columbus Georgia, Hartford Connecticut, and western Massachusetts over a two-year period. The second cohort consisted ove an additional 1100 students were recruited from 16 Technical High Schools in Connecticut. A third cohort consisted of over 600 students from 9 middle schools and 10 high schools from outside of Connecticut with high proportions of military dependants.