Are CLIL texts too complicated?

Abstract This article presents a comparative study of the linguistic characteristics of some materials used to teach English as a foreign language, and Geography and History through English in a Content and Language Integrated Learning (CLIL) experience in the Basque Country with students aged 11–13. This paper analyzes and compares the contents of current textbooks using Coh-Metrix and AzterTest, which calculate stylistic and linguistic metrics regarding lexical and grammatical complexity, readability and coherence. Finally, the study suggests that there are significant differences mainly in vocabulary level, narrativity and cohesion, it identifies the potential difficulties of CLIL texts and offers advice on how to overcome them. Raising awareness of the complexity of some texts used in CLIL can provide a starting point for pedagogical adaptations and contribute to optimizing learning.