I only had 4 boys in my den. Each boy had about a 4-foot length of ¼” or 5/16” braided nylon cord. I kept the cord. I would demonstrate the knot a few times. Then I had them tie the knot with me one step at a time. We did that until they all got it. Then I had them tie it on their own. The boys think that if they get it once they know it. Often if you ask them to do it again they fail. I would have them tie the knot several time on their own. For the boys that were having difficulty, I would help them one-on-one until they could tie the knot. It is amazing how hard knots are to teach, even the square knot.