I used nat.teachers for individual tutoring for some time, one is really good and one kid benefited from it, not that much I believe when comparing having this tutoring or not.. the other kid not difference when comparing to my effort to teach her english.
500 per hour, that's too much and not very effective. I stopped, used my own method, better than those native ones!
The kids with good accent need to have a right learning envirnoment when they started picking up their oral language skills, for example, when they are in nursey will be a good timing. A school has a NET and good interactive curriculum could help the kids develop their English accent.
As parent, we could encourage them to speak English in public. The best way is always speak English in everywhere. Some may feel embarrass and think they are not good in their non-mother tongue. But if this is good to our kid, nothing to lose, right?