High school students in the U.S. (N=1,078; 47% boys) responded to survey items on their self-esteem and interest in schoolwork, their personal expectancy of high school completion, and their perceived support from parents, teachers and peers for their expectancy. Their GPA and days absent from school were collected from school records. Personal expectancy, parent, teacher, and peer support all had significant positive impacts on students' self-esteem, interest in schoolwork, and GPA. The pattern of effects was consistent across the subsamples of Grades 5 to 6 (n=264), Grades 7 and 8 (n=226), and Grades 9 to 12 (n=319). Positive personal expectancy and teacher support also had significant negative effects on absence from school for Grades 7 and 8. Of all the significant others considered, support from teachers had the strongest impact on self-esteem, interest, and GPA in the high school subsamples. Teachers are probably the most influential agent in promoting self-esteem, interest, and academic performance in the school context.