A very sensible balanced response from Perryman.
Assuming that you are not in the big money for St Dunstans (£14,061 per year, mutiply that by 5 or 7 years), then there is quite a baffling choice.
The BBC website has secondary school league tables, but then do you go for the five GCSEs score, the English Bacc score, or the Value Added score, or a smaller school, or a speciality school?
Lewisham has a lot of single sex schools: better for girls, not so good for boys? Also faith schools, as well as the private sector. Most are doing pretty well, but like every school they have good and bad years.
Then there's Southwark, Greenwich and the green pastures of Bexley, Bromley and Kent. Education officers talk about "imports" of children from Southwark, and "exports" to Bromley etc: so children tend to travel out from the centre, while many workers travel in to central London.
My choice several years ago was for a mixed school (now completely reorganised, rebuilt and with different staff), not too far away (so that they could easily visit their school friends at weekends and in the holidays) with some enthusiastic teachers who would develop all their talents. League tables and Ofsted reports provide a good picture, but you can't beat visiting and asking plenty of questions of the staff.
And don't write off a school just because the pupils are very noisy at the end of the day, in the streets or on the bus!