There are two types of special ed. One is for example for the child who has trouble pronouncing words or reading ,while he other is for someone developmentally disable. It is the developmental disable that cost between $40,000 in a public school to $140,000 in a private school.
Each and every special ed student is evaluated by the board of education and a plan is made as to how he or she is to be educated. If the parent agree then the child goes to public school. If the parent disagrees they get a lawyer and they must convince a judge that the public school is not in the best interest of the child. The easiest way of proofing this is that the public school doesn’t speak the child’s language.
As to the question do any of these special ed students understand English? The answer is probably yes but their lawyer shows in court, that they only speak Yiddish thereby requiring private placement. You must realize the lawyers take these cases on contingent. If they win they get paid by board of education if they lose the case they get nothing.
As to the claim that public school only have to teach in English and/or Spanish. A normal child who only speaks a foreign language and is not being taught in that language can and will be granted private placement otherwise you are just warehousing him not educating him.