While on Koh Lanta, I went to two cooking classes: one in Saladan, and one on Klong Nin Beach, Roi Thai. Of the two, I recommend Roi Thai.
I went on a Friday, when we went to the local market to buy produce, fish, and other products. It was most educational. Our host told us about Thai food in general, ingredients, and preparation methods. It was good to see the ingredients at the market, AND to see what the chef bought for later. He also provided us with a couple of street vendor appetizers that were very nice.
Back at the cooking school, we all did everything ourselves, from cutting up the ingredients, grinding the ingredients and spices, and cooking all (except one little bit) of the food before we tasted it. I wasn't fond of the deep-fried spring rolls (a long-standing dislike), but the rest of the menu was great. The fish was exceptional.
There were only three of us in the class, one of the things that made it memorable. A previous review indicated he(?) was the only one in a class, and he was not happy. So I would recommend finding out how many are in a given class before signing up. I didn't, but I was lucky. Six or less participants should be a very good class.
I recommend this to anyone who is interested in learning about Thai cooking or wants to improve their knowledge about Thai food and its preparation.