The purpose of this study is to present the most salient conclusions of a study that analysed the extent to which language contact has modified the varieties of Castilian spoken in Catalonia. The research combines qualitative and quantitative methodologies, and is carried out from a structural point of view. The material gathered is a set of informal interactions produced by school-aged subjects. Results show that the amount of language contact phenomena remains extremely low, less than 2% on the whole. Considering the composition of the sample (pupils from a range of schools around Catalonia), it can be said that the increase in the use of Catalan in education has not modified the Castilian spoken by children.