This study examines the interaction between learner-oriented codeswitching (CS) practices and the degree to which intermediate Chinese L2 learners of English engage in classroom interaction. The guiding questions are whether the teacher's CS use facilitates classroom interaction at moderate L2 proficiency, and if so, at which specific stages of the lesson, and to what extent. A systematic comparison of two classroom types was carried out in the same Chinese secondary school, with English-only instruction versus with English-Chinese CS. A combination of quantitative and qualitative analyses was based on class observations (two classes per type) and subsequent teacher interviews. CS behaviour was analysed in relation to the particular teaching focus of the task at hand. Interviews included a stimulated recall technique using selected CS extracts to enrich insights from the teachers' perspective. The results showed a higher student response frequency as well as a longer mean utterance length in CS classes. Overall, codeswitches were systematically distributed across lesson stages and were closely related to changes in the teaching focus. These findings call for an optimal use of CS in instructed environments so as to maximise its benefits via a sensitive adjustment to specific pedagogic aims.