Now that's a provocative title!
Why? Here's what I think (warning: opinion).
A significant proportion of private school students do not live within walking distance of their schools. Or, even if they do, Mum and Dad are so paranoid they won't let them walk. (Kids are always angling for a lift to school... I did!)
I think it likely that a higher proportion of children attending state schools live within walking distance. The quality of a school is a significant factor in the decision about where to live. If you're going to send the kid to a state school, you'd like to be close to it. The same is probably true for many parents who favour private schools, but since there are other factors -- like which hokey religion you subscribe to, and which school Daddy and his old boy mates went to -- chances are you can't find a school to your liking close by. Quite a lot of prestigious schools are in areas where hardly anyone can afford to live and since you're sacrificing your arse to send your kid to one of them... You get the idea.
The alternative is, of course, public transport. One sees a lot of children in uniforms on trains, trams and buses. But an awful lot don't go by public transport, either because public transport is hopeless or it takes too long.
(Guilty! It takes me at most 30 minutes to drive to work, even in the worst of peak hour. Walking and catching three buses would take at least 90 minutes and cost me three times as much.)
So they drive.
A lot of them are driven in hulking great SUVs.
So, to summarise...
- Greater distance to school
- Driven, rather than walking or catching public transport
- In an SUV
QED. Private schools contribute more to global warming than state schools.