How much is the direct?
The flight from London to Boston should be roughly 7h30, the Dublin stop makes it around 10h30. I think the immigration process should be well under 3 hours so I'd probably prefer a direct if prices were same.
I am all for the Scouts doing a cookie drive or organising a local car wash. But I draw the line at them flying transatlantic aircraft so they can raise money for their new scout hut.
Also you'll do USA Customs in Dublin, saving you time in the USA.
Effectively BA tickets, Aer Lingus flights, the transatlantic portion operated by ASL on an Aer Lingus 757.