Fmm, I think you are definitely right that in West Beckenham you'd be outside the Langley catchments. That said, Harris has taken over the schools which serve that area (Cator and Kelsey) so they'll probably be improving. Worth investigating. There are other grammar schools - eg in Sutton (Wallington, Wilson's, Nonsuch, Sutton) - not sure how you'd get there! Maybe the Croydon Tramlink which stops nearby? The Harris City Academy near Crystal Palace gets brilliant results and is quite close. The BRIT school is another option? Archbishop Tenison's CofE school near Croydon is said to be good (a friend's daughter went there).