The first expedition took nineteen students and three staff. This year's took ninety-four, in three cohorts, and the logistics document runs to forty pages.

The academic case is straightforward: glaciology, altitude physiology, high-desert ecology and Himalayan trade history are all more legible when you are standing in them. Students collect data that feeds a term of work back at school.

The other case is harder to write in a syllabus. There is no signal in the valley. For six days a class of fourteen-year-olds has nothing to do in the evening except talk to each other.

Every year, staff report the same thing on the return journey: the social geography of the year group has quietly rearranged. Students who were peripheral in September come back central.

We do not claim to have engineered that. We simply keep booking the buses.