Many students learning English speak it quite fluently and seem to be proficient.
School, however, demands a more sophisticated variety of English, both read and written. Thus, even fluent speakers could require ESL to provide them with the appropriate language experience that is unavailable outside the classroom. ESL is a transitional service rather than a subject. Students are in the process of learning the language of instruction and in many cases, the content matter of subjects appropriate to their grade level. Thus ESL does not have a specific curriculum.