Teaching EAL/D students in the middle years
In Australia, Canada, UK and US where there is large scale immigration, it is common to find students in schools learning English as an additional language or dialect (EAL/D) while learning in it. In Australia over 25% of all students learning in schools come from language backgrounds other than English (LBOTE). They may have just arrived literate and fluent in the first language or they may be second generation migrants who entered school with little or no English. For all these students learning to speak in English to accomplish day-to-day interactions develops quite rapidly. However without explicit support these same students will not achieve success in the academic registers of schooling even after 5-6 years in mainstream classrooms. For while English speaking students are building on their knowledge of English to develop the appropriate language required for academic learning, their EAL/D peers are not. In addition, the conversational fluency of many EAL/D learners may mask their real language learning needs, needs that may in fact be perceived by their teachers as a "learning difficulty" or "low ability".

English language support is therefore needed far beyond the first year of arrival or the early years of schooling.

Gibbons, Pauline. Bridging discourses in the ESL classroom: Students, teachers and researchers. A&C Black, 2006.

Since the early 1980's studies have shown that, despite the rapid growth in conversational English, it takes far longer for EAL/D students to master the academic language of schools to that of their native English speaking peers. This is particularly an issue for students who do not have well developed first language and literacy skills. (see for example Collier 1989, Cummins 1984, 1996, 2000; Hakuta et al 2000; Mackay et al 1997)
BICS & CALP
According to Cummins (1984), there are 2 stages of language proficiency. The first stage includes Basic interpersonal Communication Skills (BICS) and the second stage is Cognitive/Academic Language Proficiency (CALP). It takes 1-2 years for a new ESL student to be fluent in the first stage (BICS) and 5 – 7years for an ESL student to develop proficiency in CALP with ESL support. While the stages are sequential they may overlap in acquisition.
For more information see http://grammargraph.wordpress.com/2010/06/09/academic-and-social-language-implications-for-language-in-education/