There are a bunch of different options in the Napa Valley. Some are demonstrations. Some are hands on. Some are part day. Some are all day. Basically you can pretty much find what best suits your needs.
We liked the idea of market classes - where you source and cook with ingredients that are fresh and locally harvested. Cost and timing weren't in our favor here. A few half day courses cost $250 to $350 a person - that ruled out a lot of schools. Many farmer's markets start wrapping up the season in late September/early October - that limited the type of cooking we could learn about.
We decided to go for more of a cooking boot camp - a 3-day retreat in Calistoga (Gourmet Retreats at Casa Lana) where we refresh the basics and tackle sauces as well as harvest herbs, vegetables, and fruits from the garden (each 5 hour course works out to be about $217 a person. The programs we considered before making our final choice were: