I agree with you on the part that the human selects the type of dog they would like to teach their dog something in a schooling session. The place i dont agree is that the humans hand in it stops there. For example if your dog was rolled 3 times with all 3 opponents were front end dogs and all your hound ever learned in those 3 rolls was how to tuck his front legs. You decide for his next roll you want him to face a backend ace. What you are doing is trying to expose your dog to a different style(school him). Lets say when you release your dog the backend ace runs his scrarch and for the first time in his life he immediately tries to take a shoulder hold and never gets to touch anything for the duration. Your dog has still only experienced front end dogs. Yes the human can choose the opponent but the human cant make the opponent fight a certain way. Thats why i say its the opponet teaches the prospect. He gets exposed to a senario and its up to him whether he learns/adapts to it.