In the first part multilingual education is identified as content and language integrated learning. (CLIL). Its origins and evolution are briefly sketched. In the second part some of the effects of CLIL teaching on primary school pupils will be discussed. It will be shown how cognitive and brain effects manifest themselves. In the third part a number of explanations are put forward. Here the role of implicit learning will be heavily stressed. Finally, the results are discussed with respect to learning language in particular and learning in general.