I am kind of amused that people would consider an immersion program appropriate only for HG+ kids, when immigrant kids at all levels of abilities are thrown into the water with often limited support and expected to figure it out.
I am a non-native English speaker who immigrated to the US over a decade ago. I don't speak English at home, and neither do my US-born, non-HG kids (at least not within my hearing!). They started formal schooling in K in a well-established Spanish immersion program. Juggling academics in three languages can be hard to balance, but they are coming along rather well, considering their other challenges.
Our district does not have IQ requirements for entrance in K/1st (after that the only kids who can join the program are those coming from other immersion programs who can show they are bilingual and biliterate at grade level). They do have a language assessment to make sure the candidates are on track for language development in one of the two target languages.
For the OP, since the program is new and you won't be able to see it in action the questions to ask are:
1) How will the instruction be structured? 50-50? 70-30? 90-10? Spanish should always be at least 50%, although you also want to make sure consideration is given to transitioning out to... whatever comes next.
2) How are the kids selected? A program which is not 50-50 (50% English speakers, 50% Spanish speakers, with native bilinguals counting on both sides) will have a harder time keeping the immersion working outside of the classroom, weakening the program.
3) How are the teachers selected? You want teachers who are natively bilingual, or a teaching team with a native speaker for each target language. Finding those teachers can be difficult.
You need a good talk with the people designing the program, not with a teacher who clearly doesn't understand how immersion works.
Somebody made (and edited?) the point that since any child who is floundering in a public immersion program has a good chance of being yanked out, there is attrition and the classes tend to concentrate higher achieving students. That has proven true, in our experience.
And yes, there is a hit to literacy achievement (there are only so many hours in the day you can spend reading/working) in the early grades. Having crunched the NCLB test stats for our district recently, they catch up by 3rd grade. But that means that this is not a one year decision. You need to be able to commit to at least six (K-5) years of immersion.
I won't touch Bostonian's article with a 10 foot pole, because the wrongness, it burns :P But yeah, if your goal is the hamster wheel of NYC private school admissions you probably want to avoid the Spanish immersion program, and concentrate on.. test prep?
