I am preparing to teach a class

at a summer school. (It is in Downunder so the class is in January.) As usual I have my concerns about being well prepared, very well prepared. Recently I was reminded - yet again - that teaching adults is quite different from teaching children.
Yes, there may be the occasional child who will say, "You're wrong". That child may go on to show they have done the research and can tell you from reliable sources that  they are indeed right and you are wrong.
With adults it is a different story. They will look something up. Some of them will look at the source of information and judge whether it is reliable or not - others won't. They will simply say, "You're wrong. I read this on the internet. It has to be right." (Yes, I know it used to be "I read it in a book.")
In beginning to prepare for the class I went back to my original sources.  These are books, leaflets, patterns, old duplicated sheets and a few letters from people  who were - and sometimes still are - working in the field. There is no reason to suppose that they always had everything right when they committed words to paper. What I am relying on of course is that the information they have given me individually is information they would generally agree on with each other. 
I have looked up the same sources on the internet if they have a presence there. Are they still saying the same thing? Who else is saying this now?
I have emailed some contacts in the area. What's their view on a certain issue? They'll get my class notes later and, where appropriate, a mention in the class of a name to look for in the area. 
Yesterday a visitor looked at the beginnings of my preparation and asked me, "Why are you bothering with all that? Why don't you just show them how to do it and let them get on with it?"
She went on to tell me "it isn't worth it" and "they won't be interested in  all that history and stuff".
I disagree. Of course I could simply show them something but that isn't the same at all. If people understand what they are doing then they will be able to repeat it later when I am not there. I might also have been able to teach them something they can use again or which will help them understand something else. 
It isn't just because people will be paying to do a class. They won't be the only people paying to do a class at the same event. It is because people will have signed up to do a class because they do want to learn something. 
Almost two years ago I taught another class at a similar event run by the same group. There was a very elderly woman in the class. She struggled and I wasn't sure I had actually managed to teach her much at all. I told her that she could have some extra help if she needed it. Her daughter promised to make arrangements if it was necessary.
Not so long ago I saw them both. No, she hadn't finished the project but she was still working on it and was, she thought, about two-thirds done.
     "I went home dear and when it was all quiet and I could think again I realised I had managed to learn such a lot."
She was relying  heavily on the notes I had prepared. 
     "I couldn't have done it without those. I'm so glad I did do the class."
That's why I'll do the same sort of preparation again. That's why it is worth trying to do the best I can.