Content and Language Integrated Learning, or CLIL, is where a subject is taught in the target language rather than the first language of the learners. In CLIL classes, tasks are designed to allow students to focus on and learn to use the new language as they learn the new subject content.
In a bilingual English/Spanish school, after a certain age half of the subjects, including maths and sciences, are taught in English.
In the classroom
CLIL materials are often characterised by lots of visual support for meaning, to allow low language level students to access high level content. The materials allow the students to focus on the language they need to learn about that particular subject in English. The choice of language focussed on is determined by the demands of the subject.