The Ramírez, Pasta, Yuen, Ramey & Billings 1991 study analyzing the achievement of 1,054 language-minority children in structured immersion, early-exit and late-exit bilingual programs has several serious flaws which lead me to conclude that we cannot place any confidence in the finding of no consistent difference in the achievement of children regardless of how much Spanish or English is used in instruction.
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Christine H. Rossell (1992) studied this question.
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