McField, G. and McField, D. 2014. "The consistent outcome of bilingual education programs: A meta-analysis of meta-analyses." In Grace McField (Ed.) 2014. The Miseducation of English Learners. Charlotte: Information Age Publishing. pp. 267-299.
McField and McField analyzed all comparisons done in all meta-analyses of bilingual education vs. comparison programs (students with similar background in all-English programs) for tests of English proficiency. Previous meta-analyses found positive effect sizes for bilingual education, ranging from .18 to .33. McField and McField reported that when both program quality and research quality are considered, the effect size in favor of children in bilingual education programs is larger, d= .41.
This should settle the argument: bilingual programs, when set up correctly and evaluated correctly, do not prevent the acquisition of English – they facilitate it.
(Note: An effect size of .2 is considered "small," .5 "moderate" and .8 "large.")