The optimal student-to-instructor ratio for advanced dive courses, such as sidemount, wreck, and technical diving, is 3:1. I never teach more than THREE (3) students per certification class. Group workshops can vary in size - depending on the subject and environment. I believe that class sizes play an important role in the quality and value of a scuba course - they determine how much attention the instructor can spare for each student, the amount of available 'practice time' for skills, and the level of safety supervision that each individual can receive. In most instances, agency standards permit much larger class sizes for instructors. The only benefit from that is more money for the instructor - sometimes that benefit is shared with students, as a cheaper course, but more often it is not. Either way, the quality and value of the course are diminished. Value for money in advanced dive training is critical - and a big class simply means that you've paid money to be floating around whilst numerous other students demonstrate and repeat their skills. I aim to give all of my students the maximum instructor-student time and attention. That's a vital component in the process of creating competent and skillful divers.