It depends upon how it’s done; there are a wide range of things done under the bilingual label.
In California, it was essentially warehousing non-english speakers until they aged out of school. It was sold as temporary heavy immersion to keep them caught up until their English was adequate for regular classes, but that wasn’t what happened.
When the proposition to end it came about, there was the initial shriek of “racism”–and then even casual inspection showed that it was lead by parents of the purported “beneficiaries” of the programs, upset that their children weren’t getting educated.
My own encounter (before the initiative) was as a volunteer tutor in Alviso (a very poor area).
This kid came in with an extremely elementary list of vocabulary words (e.g., shoes, shirt) that he needed help with! He didn’t have even that much Spanish–yet he was thrown in these classes because of his last name.
And then there were the frequent lawsuits by parents to get their kids out of the “bilingual” classes and be taught in English. They were put in the classes in the first place, over the parents’s objection, because their last names ended in “z”, or other “Mexican” names . . . AFAIK, the parents won every single suit . . .
I’m not saying the you can’t have a wonderful and useful program, but be careful . . .