Thanks Mystery, this bit was interesting...
Over 3,000 out of County children travel into Kent Secondary schools (predominantly grammar schools). This figure includes approximately: 800 children from Medway, 1,300 children that travel into Dartford from London Boroughs (mainly Bexley Borough), 250 that travel into Tonbridge and 500 into Tunbridge Wells.
Only around 30% of children resident in Sevenoaks attend mainstream Secondary provision within Sevenoaks District; approximately 1,100 travel to Dartford, 1,300 to Tonbridge and 750 to Tunbridge Wells.
That is a lot of additional mileage for some children.