<p>This study aimed to classify subjective well-being (SWB) among first-year middle school students using latent profile analysis and to examine variables associated with profile membership. Data were drawn from the Longitudinal Study of Gyeongnam Education, with gender, academic competitiveness (AC), and self-efficacy (SE) included as predictors. Three latent profiles emerged: a Vulnerable well-being group, a Moderate adjustment group, and a Resilient well-being group. AC and SE were significantly associated with profile membership, whereas gender showed no significant association. Higher SE was linked to a greater likelihood of belonging to the Resilient group relative to the Vulnerable group. In the Moderate group, both AC and SE were significant predictors, with increases in these variables corresponding to higher probabilities of membership. These findings underscore the role of AC and SE in understanding variations in students’ SWB and offer practical implications for supporting students during the transition to middle school.</p>