Sorry, I'm not really able to provide a recommendation but...

I'm sure there are outdoor centres / activity providers that offer air rifle shooting so it would be interesting to see what they use.

I would be surprised if it was anything from Weihrauch.

Given the age of the students, something lightish might be wise so I'd be thinking plastic rather than wooden stocks. For me, plastic also has the advantage of being something that I wouldn't be too precious about. A dink in a plastic stock doesn't elicit the same sharp intake of breath from me when compared to a dink in a wooden stock.

Yes, I know we all want a lovely trigger, but how important is that for this application?

Having said no recommendations, the only rifle I've owned that might fit the bill is the 900x (yes, I know, I've just contradicted one of my points above) or a plastic variant. Cheap, light, accurate and a proper rifle. I also shot a Webley VMX once which wasn't awful and I reckon I've tried the odd plastic Hatsan as well which also wasn't awful.

Rob.