This study examined how perceived social support from parents, classmates, and teachers jointly and uniquely predicted psychopathology (i.e., internalizing and externalizing symptoms) and wellness (i.e., life satisfaction) in a sample of 390 middle-school students. This study also explored the protective nature of high student academic achievement in the relationship between social support and mental health. Social support was a significant predictor of all mental health outcomes, particularly life satisfaction. Although classmate and teacher support were significant unique predictors of students' internalizing and externalizing symptoms, respectively, parent support emerged as the strongest predictor of all indicators of mental health. Academic achievement moderated the direction and strength of the relationships between externalizing behavior and (a) classmate support, and (b) parent support, respectively. Specifically, classmate support emerged as adaptive for average- and high-achieving students only, whereas academic achievement functioned as a protective factor against the manifestation of externalizing psychopathology among students with low parental support. Implications for school psychologists and directions for future research are discussed. © 2011 Wiley Periodicals, Inc.