I haven't taken the
cooking class at May Kaidee's vegetarian restaurtant, but I've eaten there. Recommended.
I've taken the vegetarian Thai cooking class at May Kaidee's twice (once myself and once on a return trip to Bangkok with a friend). I thoroughly enjoyed the experience both times, though anyone taking the classes should go in with the right expectations about the environment. The location is in the backpackers section of town and the "classroom" is basic, with one side is completely open to a side street, and the recipe set you take home is just stack of photocopied pages. About half the students seem to be college-age, perhaps on their around-the-world backpacking adventure. While I haven't been to the Blue Elephant, I expect this is a very different experience.
Of course, what's important with a cooking class is the cooking and the food, and that is definitely the focus of the class. After a trip to a market to learn about the ingredients being used, the group gets right down to business. The classroom has a cooking station for each pair of students, with a wok, utensils, and bowls of prepared ingredients. Over the course of the next three to four hours, every group gets to prepare and eat 10-12 recipes from Tom Yam soup to fresh vegetable spring rolls with peanut sauce, and the food I've made there tasted better than what I found in better Bangkok restaurants. The very open, relaxed environment encourages everyone in the class to interact, and the class ends with everyone singing a Thai song together.
One thing you might find missing from the class is actual instruction, but I never found it lacking either as Thai recipes like these don't require a great deal of technique. I don't think I would have gained much from watching a chef prepare these recipes first, so it seems better that most class time is spent with students cooking. What you do get is the opportunity to cook a wide variety of dishes with a knowledgeable Thai there to help and guide you, and to have a great time doing it.