In reply to Denni:
In my school the wall was erected by attaching the panels onto a steel framework which in turn was secured to the wall itself. The whole thing was done by Enterprises who advised and sorted the structural survey. By having panels you can obviously change the holds/reset routes.
I guess holds could be attached directly to brick but you lack the flexibility to alter things..... Though costs will be much lower.
PS I am retiring soon and so if you are a geography teacher, or possibly a biology teacher, who wants 'their own' small wall to look after, then mail me for details. Midlands !