I'm a 4-H volunteer who leads quilting and sewing clubs. I can spend (and often have) a whole day preparing for a 2 hour meeting with the kids, prepping supplies, writing and printing instructions (with pictures), briefing the other volunteers. Then spend another hour or two rehashing and summarizing what was just taught so the kids can finish up...
Most workshop and class instructors are worth every dime you pay to take the course.