In reply to mypyrex:
I'm not a mountain guide, but I am a tour guide and an ML. I've lead quite a few walking groups on things like the coast to coast (I live at one end!)
There isn't one prescriptive 'do it this way' sort of guide. I always make sure that I talk to everyone and find out what their interests are so I can point out things they may be interested in on the way. Others are just interested in going as quick as possible to the next check point, B& B whatever. Some are obviously just happy walking with their partner, others like going off ahead regardless of the pace of the rest of the group, others tend to go a bit slower for various reasons. (loo breaks being one).
So if someone is going too far ahead I'll ask them to wait at some obvious point ahead, although sometimes you feel like banging their heads together when you've asked them to slow down yet again, other times you've got to encourage the slower ones to be a bit quicker if you;ve got a pick up or B& B to reach by a certain tim,e and so on.
Obviously its up to you as the person in charge to make sure people are safe, but if you've got to know the group you've got to make judgements along the way. So sometimes the group does get spread out and folk are out of sight.
As long as I can answer the "What if this happens" question then I am doing my job even if that means sometimes I'm walking on my own at the back, middle, front or simply on my own letting people chat amongst themselves whilst I concentrate on admin, map reading, looking out for hazards, what the weather is doing and so on.