This study examined the effects of a recreation activity staged according to self-determination theory (SDT) principles on in-situ vitality and in-situ affinity toward nature of teen-age male students (age 14-17) enrolled in a residential treatment program. Procedures involved staging snowshoe tours for three groups of students. Each of these groups participated in snowshoe tours on two occasions. During one of these, a variety of techniques were used to engage and satisfy students' psychological needs for competence, relatedness, and autonomy. The other tour was conducted using a traditional approach; no special techniques were uniquely or deliberately employed to address students' psychological needs. The design was counterbalanced; one group of students participated in the SDT-staged snowshoe tour first and, one week later, participated in the traditional tour. Two other groups followed the opposite pattern. Measures of in-situ vitality and in-situ affinity for nature were taken on six occasions during each of the tours. Results supported the hypothesis of a significant treatment by treatment-order interaction. Students who participated in the staged experience first reported greater in-situ vitality and affinity for nature than the groups of students who participated in the traditional tour first. When the SDT-staged tour followed the traditional tour, however, students' reported experiences were substantially lower than in the other treatment conditions. (Contains 4 tables, 2 figures, and 1 note.)