Teachers in Hong Kong Content and Language Integrated Learning (CLIL) classrooms appear responsive to students' existing linguistic repertoires, as they employ a notable amount of L1 to clarify the subject content, communicate with, and enlarge the L2 metalinguistic awareness of students with restricted (English) L2 proficiency, whilst employing little L1 with students very competent in L2, chiefly to offer translation matches for L2 subject-particular lexical items.