This study sets out to explore the effect of proficiency and modality of interaction on code-switching (CS) amongst two groups of Spanish-Catalan learners acquiring English as a Foreign Language (EFL) in Primary school (grade 3, n = 24 and grade 6, n = 21). Data was retrieved from audio-taped oral activities (peer interaction and learner-teacher interaction) in real class situations and analysed for the number of switches, their types and functions, as well as for the source language of the switch. Results show differences in the total number of instances of CS and their types and functions according to both proficiency and modality of interaction, although with no statistically significant differences between the groups. As to the source language, Spanish was found to be the preferred language for students when working in groups, whereas Catalan was used to interact with the teacher. Results are discussed in the light of the new plurilingual approach recently proposed for the teaching of additional languages in the school curriculum and some pedagogical implications are drawn as to the need to redefine teaching methodologies and adapt them to current trends in education.