We should not assume that non-native speakers who have attained a high degree of fluency and accuracy in everyday spoken English have the corresponding academic language proficiency. This may help us to avoid labelling students who exhibit this disparity as having special educational needs when all they need is more time. The non-native speakers in your classes, who have exited from the ESL program, are still, in most cases, in the process of catching up with their native speaking peers.
Common underlying proficiency (CUP)
Jim Cummins also advances the theory that there is a common underlying proficiency (CUP) between two languages. Skills, ideas and concepts students learn in their first language will be transferred to the second language.
Briefly stated, Cummins believes that in the course of learning one language a child acquires a set of skills and implicit metalinguistic knowledge that can be drawn upon when later working in another language. This common underlying proficiency (CUP), as he calls these skills and knowledge, is illustrated in the diagram below. It can be seen that the CUP provides the base for the development of both the first language (L1) and the second language (L2). It follows that any expansion of CUP that takes place in one language will have a beneficial effect on the other language(s). This theory also serves to explain why it becomes easier and easier to learn additional languages.