Using research data on teacher codeswitching in South Korea, this article investigates the attitudes and perceptions among Korean learners of English as a foreign language towards English-only instruction as opposed to instruction which contains some switching to the learners' first language. The study was in part operationalized by exploring learners' attitudes towards teachers who were native or nonnative speakers of English. The authors explored a number of variables to these attitudes and perceptions, of which the most important was the students' age. From a total sample of 798 students, 311 were adults at university and 487 were children in the last year of primary school. The researchers collected data via questionnaire and, using a subsample, via interviews. Findings suggest that although both groups of learners had no clear preferences for either teacher type, neither group favoured the total exclusion of the first language from the classroom interaction. Adults were more likely to be comfortable with English-only instruction, possibly due to their greater experience in language learning, although the possibility that their acceptance was also due to higher proficiency cannot be excluded.