Research has established the significance of social achievement goals in shaping adolescents' academic engagement. However, the precise mechanisms underpinning this connection remain incomplete. In two studies involving U.S. middle school students (Study 1 N = 212, Study 2 N = 318), we explored the relationship between social achievement goals, academic adjustment, and the mediating role of social distress and loneliness. High social development goals related to reduced social stress and loneliness, leading to enhanced classroom engagement. In contrast, social demonstration-avoidance goals were linked to elevated loneliness and stress, resulting in diminished classroom engagement. While the mediation effect was unclear for social demonstration-approach goals, they exhibited direct associations with unfavorable classroom engagement indicators. These findings illuminate the intricate dynamics between social achievement goals and academic engagement among early adolescents, emphasizing the role of social distress and loneliness in shaping their classroom experience.