Of course this is one of the most important safety lessons. We read about instances of what is commonly called an AD (accidental discharge) some resulting in severe bodily damage to the shooter and some cases resulting in death of the shooter or worse an innocent. AD’s cross all shooting levels from competition, law enforcement, hunters, gun smiths and yes… instructors.
One of the methods we have used over the years to combat this is, telling the class two or three times do NOT anticipate the command to fire, and another two or three times to “keep your finger off the trigger until on target”. And for many in the class that works but there are always those who need stronger instruction.
But sad to say every now and then you’ll still have to take someone off to the side and “instruct them further”. Instruction can vary from having them take their equipment off and watching the rest of the class, up to taking their equipment off and going home for the day to “think” about the problem they are having with the instructions. Of course this depends on the length of class and the only thing that it guarantees is that you and the other students stay safe. For the most part that will solve the problem 99.9% of the time. It seems harsh but the alternative is just not acceptable.