This article draws on a case study of 6 student teachers in secondary schools and their codeswitching between the first language (L1) and the second language (L2) over the course of 14 foreign language (FL) lessons, where French was the L2 and English was the L1 of the learners. It describes how the student teachers had been exposed to theoretical positions and empirical studies on this issue during their 36-week training programme. It analyses the quantity of L1 used by these student teachers as well as the reflections and beliefs of 2 of the student teachers on the codeswitching process. The findings reveal comparatively low levels of L1 use by the student teachers and little effect of the quantity of student teacher L1 use on the quantity of L1 or L2 use by the learners. They also reveal very little explicit reference by the student teachers to the research and professional literature they had read, yet their decision making did not necessarily stem from their personal beliefs. Some aspects of codeswitching appear to be a source of conflict for the student teachers while others do not. Implications for teaching are drawn.