With the intention of promoting plurilingualism, many European systems of education have adopted approaches that aim at integrating content and a foreign language in the subject classroom. In Poland, CLIL-type instruction is rather elitist since it is addressed mainly to the most gifted students of secondary schools. The objective of the pilot study presented in this article was to implement CLIL mathematics lessons in a state primary school in Poland and analyse the pupils' and the teachers' perceptions of implementing this new form of instruction. On the basis of semi-structured interviews conducted with the pupils it can be stated that despite the general dislike of mathematics, they held a positive view of this subject when taught in English. In the open-ended surveys, the teachers indicated that although CLIL appeared to be motivating for the pupils and contributed to the increase in certain aspects of their language competence, it failed to facilitate any progress in the content subject. Moreover, the teachers struggled with heavy workload and the lack of proper teaching and learning resources that could be readily applied in CLIL-based classes in primary school.