Real Life Writes the Plot: Elinor M. Brent-Dyer converted to Catholicism, hence Joey's conversion and the increasing religious themes in the books, particularly the Swiss era.
When World War II broke out, she realised it would be impossible for the school to remain in Austria and moved it to the UK. She also wanted to move the Chalet School back to the Tyrol when writing in the fifties, but the occupation by the Allies would have made it impossible, so she relocated it to Switzerland instead.
Write What You Know: Brent-Dyer was a teacher herself. She actually tried to start up her own school (in Hereford, which became one of the Chalet School's locations), although unlike its fictional equivalent, the school was unsuccessful in the end.
Briesau am Tiernsee, where the school was established, is based on the real-life Pertisau am Achensee.