Hey Alan,
I kind of chuckled when I saw your post as I was asked to teach flemish string portion as well for group of 16 scouts here in VA about two weeks ago. You are going to have your hands full brother and will busier than a one-legged man in a butt kicking contest. My fingers were so sore after that night.....a couple of tips that may help this go a little more smoothly:
1) Build a several string jigs as shown in the How-To/build along section of this site (I had two and things still got backed up).....or......
2) Another option (and possibly the better way) to the above would be to have 18 strings worth of material already pre-cut and then have a couple of them demonstrate the use of the jig on the last two. This will allow all of them to participate step by step as you demonstrate the twisting procedure. This will also free you up to evaluate their progress after you show them initially.
3) Serving all 20 strings will be impossible unless it is a 12+ hr. class. Demonstrating on two of the best products was all we could manage in 3 hrs.
4) They REALLY like waxing the string for some reason.
5) The hardest concept to pass along was how the counter-rotating twists hold the string together. I used a 3 foot piece of 1.5" twisted strand rope (available by the foot at Home Depot) as a large scale training aid and also mentioned that the way to make natural cordage in the woods is done in a similar way and that combination seemed to turn the light on.
6) 25% will nail it and build a better loop than you. 50% will struggle some and finally get it. 25% will lose interest and play with the wax
.
I had a blast with these young guys and I think you will too...hope these lessons-learned from my class helps you some.....happy twisting!
CPT D