The author uses a theoretical account rooted in TEFL, language acquisition and educational psychology to provide the basis for the development of a comprehensive model of language learning in CLIL. It incorporates prior knowledge, EFL self-concept, interest in EFL classes, verbal cognitive abilities and contact to English. This model is used to estimate the effects of CLIL in the context of high-intensity programmes at German Gymnasien. The statistical evaluation of the quasi-experimental data from 1,000 learners proves the existence of large initial differences due to...