I briefly looked at the linked thread, I think the kind/loving way is best. I also believe strongly in meetings starting on time. For some it can help that "set up and socializing starts at 9:30, class time starts promptly at 10:00". And then you have to hold firm to that. You have to plan in breaks and for the late people they have to be told that "follow the best you can with the rest of the group, and you will have to catch up at the breaks" then you move on. And then while the others are doing the steps required you can help the slow pokes. It's ok to acknowledge the late comers, smile at them and say "Class has already started, please set up quietly and I'll be with you at break".
I've taught classes before and I always do practice pieces so I know the time required, but classes always take twice as long as my solo time! (That's good for me to know and now I plan it in.) The instructor also needs to be keyed in on the class and if everyone gets it or not. If people are looking confused, it's up to the instructor to clarify it. If they are talking to each other because they are having problems, it is the instructor's problem... If they are talking quietly and non-disruptive, best to let them be but when it becomes disruptive I find it helps to say things like "Oh my goodness, I'm getting confused with all the discussions going on, where did I lose you?" and call attention to the problem without pointing fingers and casting blame.
I'm also a big believer in hand outs that spell out things very clearly and concisely, probably comes from spending most of my working career with engineers. Sure, a lot of things are very very easy to show, harder to write down. But having a class requirements list with basics on it like "This class is for beginning quilters. You should know the basic operating instructions for your machine, how to thread both top and bobbins, instructor will not be able to help with machine questions. You need the following materials (I find a list works better than a run on sentence)" etc. is vital. It's a challenge for me sometimes because all I need is a diagram of the finished product to do something and others need everything from yardage amounts and cutting instructions, reminders of the 1/4" seam allowance, and on and on. So when I write up directions I try to strike a balance from what I expect people to already know (a lot!) and being clear without being insulting.
And then everyone should know exactly what is going on. Sometimes people are under the misunderstanding that it is a discussion group and not a class -- and sometimes the leader is confused that it is a discussion and not a class
We all have different gifts and different ways of seeing things. One of my dear quilting friends is known for always being late. We could get angry, but what we've learned to do as a group is to pick her up (early) so we can get to where-ever on time and accept her arrival at small group whenever it happens. She also has a hard time following printed directions but once talked through the steps can work away for that session. If she doesn't finish she has to be talked through again the next time. It's just the way she is, but she is the nicest, kindest, sweetest person and a joy in my life even if she requires a tiny more bit of effort than some of the others.