Informed by a mixed methods research design, the study investigates the interrelations between students' attitudes toward English learning, English-medium instruction (EMI), and the use of their first language (i.e. code-switching) in relation to a range of biographic and contextual factors in their situated EMI programmes. The quantitative analysis revealed a positive correlation between students' language learning attitudes and EMI attitudes due to their strong instrumental and integrative orientation, while the qualitative results further demonstrated the socialising effects of EMI which strengthened the students' positive attitudes and motivation. Additionally, correlated with their instrumental orientation toward EMI, code-switching was deemed highly necessary by the students, but it would need to be carefully planned and implemented together with other instructional strategies and resources to promote effective content learning. Despite the varying attitudes among the students from different backgrounds, the current ideology and discourse surrounding EMI (e.g. linking EMI with academic success and career prospects) might counteract the influences of other personal and contextual factors and sustain the students' positive attitudes. The study concludes with practical implications for EMI teachers and curriculum designers on how to create an effective EMI classroom with reference to students' multiple and dynamic language attitudes.