This study aimed to investigate the association between general science teachers‘ effectiveness (TE) in teaching through English, their emotional intelligence, and students‘ academic success. In addition, it sought to determine which dimensions of English as a medium of instruction (EMI) and teachers‘ emotional intelligence (TEI) accounted for the greatest variability. Furthermore, it examined whether demographic variables such as sex, qualification, and experience co-variated with students‘ academic achievement (SAA). To achieve the objectives, a non-experimental correlational design, adopting a convergent parallel mixed method was employed. The study sample included 45 randomly selected teachers and 1575 students in 45 classrooms. A teacher-effective EMI use questionnaire, the Bar-On-EQ-i, classroom observation protocol, semi-structured interview, and an academic achievement test were used as data collection tools implementing the principle of the value-added and Bar-On-EQ models. Frequencies, means, and standard deviations, Pearson product moment, standard and hierarchical multiple regressions, and Kruskal-Wallis Tests were computed using SPSS version 26. Inaddition, confirmatory factor analysis (CFA) with an AMOS graphics was applied. The findings revealed a strong relationship between teacher effectiveness in teaching science through English and students‘ academic achievement [r =.59, n = 45, p <.01]. Moreover, the composite result indicated a moderate and significant relationship between total TEI and SAA [r =.424, n = 45, p <. 01] while pedagogical knowledge being the highest contributor and experience co variating with SAA. Although TEI could show 23 percent variability in SAA, it was found to be non-significant predictor of SAA, F (5, 39) =2.37, P <.057. The study recommends on-the-job training for EMI teachers. Additionally, experienced teachers should work in collaboration with younger teachers and share fresh perspectives on teaching methods and effective language use. The introduction of EMI implementation policies is also recommended