Emotional intelligence (EI) is closely connected with mental health, academic achievement, and social adaptation. The purpose of this cross-sectional study is to evaluate EI and explore its associated factors in Chinese adolescents in school. Self-reported questionnaires were distributed to participants--a total of 2,058 students aged 10 to 18 years and 114 homeroom teachers. A hierarchical linear model was used to test the effects of individual and class level variables on EI, respectively. The study found that the participants exhibited slightly higher EI scores than their Western counterparts and that EI levels varied between classes. Students' prosocial behaviors, study pressure, left-behind status (at the individual level) as well as the homeroom teachers' gratitude, job rewards, negative teacher-student relationships, and perceived organizational support (at the class level) were significantly associated with EI. Therefore, the emotional expressions and working situations of homeroom teachers should be promoted to facilitate the development of adolescents.