We examined (a) the relative importance of perceived social support from parents, peers, and teachers; (b) the consequences associated with different types of perceived social support; and (c) the mediation by achievement goals in the relationship between perceived social support and academic outcomes. We analyzed the first 3 waves of the Korean Educational Longitudinal Study 2005 data (Y. Kim et al., 2007), which followed students from Grade 7 to Grade 9 in middle school. Compared with the other 2 social agent groups, support from parents predicted the widest variety of adolescent motivation and achievement indexes. Parental emotional support was most beneficial, predicting stronger mastery goals, weaker performance-avoidance goals, lower test anxiety, and higher academic achievement than any other type of support. Parental academic support functioned as a double-edged sword, predicting not only stronger mastery goals but also stronger performance-approach goals, stronger performance-avoidance goals, and higher test anxiety. Achievement pressure from teachers had the same predictive relationships but was weaker in strength. Perceived emotional support from teachers was not as effective as that from parents in predicting adolescent motivation achievement; however, perceived academic support from teachers was helpful for adolescents in predicting stronger mastery goals. Support from peers worked as a buffer against maladaptive motivation, predicting weaker performance-avoidance goals and lower test anxiety. Mastery goals mediated the relationship between social support and academic achievement, whereas performance-approach goals and performance-avoidance goals mediated the relationship between social support and test anxiety. The same patterns emerged consistently for all 3 years at middle school.