I'd suggest there are at least three issues which need to be separately discussed in this context: A) which type of teaching (bi- or mono-lingual) more quickly/effectively brings the student up to speed in English; B) which type of teaching has the less negative impact on the student's learning other subject matter while they are learning English; and C) which type of teaching best enables the student to also maintain their original cultural/ethnic identity and value their original culture, as well as American culture. I think these three issues often get muddied and confused in the discussions on this topic. I would also expect/hope that at least some evaluation/empirical studies would have been done on these three issues, and would hope that discussion would reflect, at least to some degree, the results of those studies, rather than just people's personal experiences or subjective opinions.