RE: Trying to choose a board for my kids...
Which form of "tethering" do you want to try?
The "between two boards tether, or a "static" tether.
For a "static tether", I drill a small hole near the tip of the
center fin on the older starts.
A 1/8" hole does not affect the performance of the center fin, and you
can tie a small loop of line through the hole to attach your static tether line.
Be sure to attach a small lead "sinker" (you can get them at fishing supply stores or commercial marine chandlers) so that your tether line
hangs straight down from the fin (or the tether attachment on later Starts and Rio's) but does not touch the bottom.
Then a good sma;; muchroom anchor worked into the bottom until it's fully covered, and you have a self suffcient static tether system.
If you are wanting to try the "between the boards" tether system, that consists of about 15 feet (5 m) of line with a short section of "bungee" chord tied in the middle. So, you have 2 pcs of 1/4-3/8 " line about 7-10 feet long and a 12-18" piece of 3/8" bungee in the center.
Tie the line to the mast foot on the "instructor board" and tie the other end to the hole in the nose of your older Start that your students will be on.
Tell the students their "job" is to sail well enough to keep slack in the line.
The idea here is not to "tow" them, but simply to give the instructor some control to prevent the student from sailing off downwind.
This works really well because the 2 boards are at a conversational distance apart (no yelling required or desired) and the student has only to look at the other end of the tether line to see how the instructor uses stance, foot position on the board, sheeting angle, clew position, etc. make the board go where they want it to.
I find that < 10 minutes is all it takes for most students to pick up enough basics that they can be "set free" to sail around on their own.
Hope this helps,