Actually lots of schools with higher migrant density are high performing schools. It is the case in WA, where 2 of the top 5 state schools are situated in high immigrant populations. Migrants don't automatically translate to lower performance in school, nor do they always equate to lower socio-economic areas. So to say that parents don't send their kids to a high migrant density school because of lower performance doesn't actually stack up.
Migrants may or may not speak English as a first language so to generalise about schools with migrant populations isn't helpful IMO. High-performing schools where English is not the first language of most of the pupils may exist but they are probably the exception. Happy to be proven wrong, that's just my understanding.