The major difference is that the coach is on your back everytime, and that's one of the things that makes the most progress. The exercises are also specific to your problems and those of your horse rather than to the majority of a group. Progress is fast and effective with a particular teacher, a session can be more rewarding than a dozen in group. Indeed, it’s at a price, but the best is still to work with several professors, who will not have the same eye and identify different and complementary problems. After that it is on that the private lessons are less convivial than the group lessons because you are alone, but you can give yourself thoroughly during your class. After all depends on your goals. In terms of time, it's an hour or an hour and a half, after it's too long for you and your horse!
Bye and good individual class ;)
When you start taking individual classes all the attention of your trainer is focused on you. So he/she can make you a personalized planning to improve your riding skills.
If I wanted to take a private lesson, I would like the instructor to really adapt his lesson to my level and my horse's abilities and take the time to explain things to me.