Grit has been defined as passionate perseverance toward long‐term challenging goals and it is associated with various positive outcomes for youth, including academic achievement. However, less is known about these associations for the two facets of grit (i.e., perseverance of effort, consistency of interest) and few studies have examined the link between grit and perceived social support. The present study examined the group‐level demographic differences (i.e., gender, grade, socioeconomic status, and special education status) of grit in a high school sample (N = 1,077). In addition, direct associations between grit and perceived social support from multiple sources (i.e., teacher, classmate, parent) were examined, as well as a potential enhancing effect of social support as a moderator of the relation between grit and academic achievement. Results indicated positive associations among grit and its facets with social support from parents and classmates. Furthermore, the positive relation between grit and achievement was stronger for students reporting high social support from teachers, but not other sources (i.e., classmates, parents). Practical and theoretical implications for promoting student success are discussed.