Many things. One of the major differences is that every class session spends about half the time with the pickers in small circles, leading themselves in jams, each circle attended by an experienced, helpful coach. I think a student can get better help being coached while they’re jamming than in a one-on-one lesson or sitting in a class listening to a teacher.
We teach a lot of skills that are normally never taught in books or lessons, such as how to lead a song, how to learn a chord progression quickly, how to fake a solo on the fly, and so on. Many jam classes I’ve seen are more about following the teacher leading everyone. We teach jam skills and repertoire that way, but the best way to get good at jamming is to practice actual jamming… so we show them how it’s done and get them jamming!