Not read all of the replies so sorry if this is a repeat.
Firstly, Richard T is definitely your man. He has many years of experience with scouts and narrow boats.
As to your point about taking scouts with behaviour issues, I agree it's scary to contemplate some with locks. And with current, 'someone's got to be summonsed' culture that is even more scary. Much of my early narrow boat experience was with school parties of mainly 10 and 11 year olds. I recall some challenging characters who gave me nightmares before we left. However, in all the cases I can recall, they responded hugely positively to doing locks, steering a 70foot narrow boat and generally being outdoors and active. I used to wish some of them could do a flight of locks before school each day. I think it's great that you are looking into getting your scouts to use the waterways and I wish you well with your project.