I was going to suggest Streatham, too. Specifically Streatham Hill between Cricklade and Wavertree. Also possibly closer to W Norwood.
Plenty of Good and Outstanding primaries much loved by the local community: Hitherfield, Streatham Wells, Dunraven Primary. Towards W Norwood: Julian’s. Secondary: Dunraven, or Bishop Thomas Grant if Catholic. Plenty of kids from the area go to the Sutton grammars, or a selective place at Graveney, or a lottery place at comprehensive Kingsdale, a bus ride away.
Lovely local park (Hillside Gardens), active community (street parties) nearby Streatham Common, Brockwell Park etc.
V quick bus to Brixton for tube, trains from Streatham Hill or Tulse Hill.
Loads for teens to do: Streatham Ice Rink, any amount of theatre, dance, music and drama projects, cinema in Streatham, Brixton, W Norwood. Theatre in Streatham and Brixton.
Or catchment for Charter, Herne Hill / e Dulwich direction?
Personally I would keep my growing kids / soon to be teens close to activities and public transport, and keep my commute short.