They're instructed on how and when to choke, spike or shock their dog. 

 Owners and dogs endure several weeks or months of chaotic classes.  The trainer is trying to explain to everyone simultaneously; this makes the owners and dogs confused and bewildered.  Picture at each lesson a room full of dogs barking or growling at each other or at other people; you hear frustrated owners trying to yell over the noise to give commands to their dog, which they don't know in the first place!  While all this is happening, the trainer will be trying to teach everyone how to correct their dog by choking, spiking or shocking!

 Combining a group of inexperienced students and untrained dogs in these conditions equals complete pandemonium. 

 Trying to teach in these conditions causes owners to ruin their dogs, possibly forever!

 Understand that dogs learn by conditioned association or repetition.  Owners will be repeatedly choking, spiking or shocking their dogs; with enough repetition, the dogs will associate the leash and collars with the pain that comes with them and will run away when they're off.  From the beginning to the end of each lesson, mass confusion occurs; unlike the expert style.  

 Obviously, the group style is the worst quality training.  How could anything positive be accomplished in this environment?  

 Anyone who chooses the group style couldn't possibly understand the quality differences between the 3 styles before paying!