Bilingual education vs. English immersion: a draw?

A review of Proposition 227's effects commissioned by the State of California has English immersion and bilingual education at a draw, according to Sarah Tribble of the Contra Costa Times (via Kimberly Swygert):

It doesn't matter whether California students who don't know English are taught in bilingual classrooms or fully immersed in the language, according to a five-year study of California's Proposition 227. What matters is the quality of the education they receive.

Some findings from the report:

"we conclude that Proposition 227 focused on the wrong issue. It is not the model of instruction employed, or at least not the name given to it, but rather other factors that are much more operative in distinguishing between failure and success with ELs."

Comparing English immersion to bilingual education, "the best analyses we have been able to conduct given data limitations indicate that differences across models of instruction—holding constant such critical factors as student demographics—are minimal or nonexistent."

"the strongest predictor of academic underperformance" is poverty.

These findings probably apply to instructional approaches for subjects other than just English language learning. That is, social, cultural, and economic factors play a greater role in academic achievement than the method of instruction. Designing curricula requires taking the local environment into consideration.