And again, what's the best way to teach ELL students?

Another study, this one from Houston, finds it's dual language immersion:

The study's findings should dispel notions parents have that their English-language-learner children will learn English faster if they're totally immersed in the language, researchers argued.

"The best way to help them learn that language involves teaching them in their native tongue," a research summary indicated.

...not only parents.