Metalinguistic skills are highlighted in the literature as supplying bilinguals with an advantage in additional language (L3) learning. The degree to which this may apply to bilingual education and content-and-language-integrated-learning settings, however, is as yet little understood. This paper reports on a study examining and comparing the metalinguistic skills of Dutch secondary school pupils enrolled in a Dutch–English bilingual and a regular programme as captured in think-aloud protocols and retrospective interviews linked to an individual picture-description task in German. The findings show that clear metalinguistic advantages for the pupils in the bilingual stream could not be established. However, the study found evidence of changes in pupils’ L3 processing linked to the functioning of the multilingual mental lexicon, a more functional awareness of language, and the pupils’ attitudes towards language learning. These findings were able to elucidate the nature of metalinguistic skills – pointing out the need for a more precise definition in particular – while concurrently disclosing the limitations of the concept for grasping multilingual language processes in bilingual education settings.