Although many advances have been made in recent years concerning the theoretical dimensions of content and language integrated learning (CLIL), research still has to meet the necessity to come up with integrative models that adequately map the interrelation between content and language learning in CLIL contexts. This article will suggest that recent models of the bilingual lexicon make a fruitful starting point for this purpose, because they stress the close interrelation between conceptual and linguistic strata. Besides a language-specific conceptual dimension, these models cater for developmental aspects of extension and restructuring of cognitive concepts, including a reciprocal relationship between L1, L2 and the conceptual dimension. Such a differentiated understanding of the cognitive structures underlying student performances is suggested as an appropriate basis for pedagogically appropriate intervention.