Petts Wood has the school coach to Dartford Grammar (and also the Wilmington Grammars)
http://www.nkst.co.uk/timetables.html . It is a lovely family friendly area, lovely restaurants, open spaces, lots of clubs, sports grounds, tennis courts, woodlands, great and varied transport links into London too (Victoria, London Bridge, Cannon Street, Charing Crossw, Blackfriars etc). Close enough to the Kent countryside to easily drive out or get the train into deeper Kent. As you are still within a London borough DCs get Oyster cards and can be quite independent getting around. Downside for Dartford is that it is a bit of an awkward journey by public transport if not relying on the school coach so perhaps not ideal but there are a number of DCs who live in Petts Wood who go to the Dartford Grammars. I had some friends move to Hextable who have a DD at Dartford Girls and they like it, it would be too small for me and no direct London trains, they head to Swanley by bus to get the train and their daughter gets a local bus which is a direct journey to the school, but they seem happy with the compromise. Whilst Swanley has a train station it quite urban and quite a few pockets of grotty areas (sorry Swanley!).