As melhores escolas particulares = The best private schools
Official translation is a bit off. Particular is rarely used adjectivally in English.
According to priberam dictionary possible translations are:
- peculiar; special
- singular; original
- private; reserved
Since particular in English connotes the meaning of "fussy" and "picky", I think it should be considered a false friend.
Unless this means they are private owners as opposed to corporations, the sentence is useless. The translations "Privates" is totally wrong. "They are particular" would be right if the sentence means the are "demanding" or "fussy." Elsewhere the word has been used to mean individual, private person, private owner, so that should be accepted.