I have taken Wilton Correspondence Courses (1970's) which I'm not sure they offer any longer. I took several local courses offered by a cake decorating store owner and his wife in the 80's. And, I just recently retook the Wilton Courses with my daughter. I also went to Wilton for their class on Holiday Gumpaste Flowers. I loved the class at Wilton's and would like to take their Master Class, but the price is a little of a set back. Maybe I'll get there someday. They do have 1-day workshops which are more reasonable. My Wilton Classes were always small -- no more than 8 to 10 people and the instructor made sure she went to each person to see if they were progressing through the Course. She was a real joy to work with. After the Course, she started a Cake Club from members of her classes that would gather monthly to make a specific cake and share ideas and experiences. Needless to say, when she had to move away, we were very sad.
I have never taken a class but would love to, however I live in a small town with only one place available for classes and they wait until they have at least 10 participants. I am a quick learner and have taught myself a lot throughout the years but I would jump at the chance to "fine tune" my skills.
To be very honest with you, I have learned a whole lot from these guys.