As far as Montessori goes... I have no idea what some people are talking about. Within 20 minutes drive time to our house there are over 70 montessori preschools. In our district there are 2 montessori public schools (and for a 20 person class, wait lists of over 300 kids for each spot), and several K-6 & 1 k-12, and 2 grade 6-12 montessori private schools. In the 5 preschools I'm most familiar with (one of which being my son's old school) there is almost NO turnover (teachers have been there for upwards of 20-30 years, new teachers are rarely taken on, although many intern for a year at these schools for their certification), and of COURSE the teachers actually teach. The teach differently than standard E.C.E teachers... but they teach and interact with the children constantly. At least the good ones do. At our school we had weekly folders that came home with their works, and daily conversations with the teachers talking about what our child had been working on educationally, socially, and developmentally that day. Far from running mad with no direction the kids are allowed to choose their own works from a *prepared environment*, on top of "focuses" that the school would also be presenting. These would vary in length according to each focus (for example The Human Body, Archeology, and Space were each a several month focuses, while Arachnids, Eric Carle, & Harvest were just a couple weeks each). Montessori can be an AMAZING philosophy & educational choice... but as with anything... there are duds out there. People who use the name, but only to get people's money.
Whew. That aside.
I think it's a perfectly valid thing to be concerned about being a minority. Because your "location" says LA, I was confused as to the whole 80% ESL thing... but your "what happened" cleared that up.
For a large part of my life I was a minority (blond haired blue eyed white girl living in Japan... much of it on an island where there were only 200 americans but the population of the isalnd was well over 1 million -aka, not a small island, but not Tokyo either). There are definite positive and negatives. The positives are fairly obvious (amazing cultural and interpersonal ones). A few negatives would include things like "no whites allowed" restaurants/ playgrounds/ etc., as well as being spit on, snubbed, and the whole pipe bomb thing, which happened more than once, although most demonstrations were fairly non-violent.
Regardless of what makes you a minority, being a minority is difficult. Whether you're the only black family, the only jewish family, the only gay family, or the only white family... being an "only" isn't easy. And there are a lot of considerations that go into doing such a thing intentionally. Especially when you're dealing with language & cultural hurdles.
Would I change schools to keep my son with a friend? Depends on the schools. Part of being a kid is learning to make new friends... and you can *always* keep old friends via play dates.