Generally speaking, the expectation is that young ELLs will achieve conversational proficiency (BICS-basic interpersonal communication skills) in about 3-5 years of English immersion, and academic fluency (CALP-cognitive-academic language proficiency) in about 5-7 (or even up to 7-10, in some of the more recent research) years. The timeline may be compressed in higher-cognitive individuals, those who are younger at first exposure to English, and those with a richer language environment (in any language), and may be expanded in those with limited English exposure outside of school, or underlying language or cognitive disabilities, among other things.
