There is an issue of the instructor & student not meshing. When I was the lead firearms instructor at our academy, we switched students every 20 minutes. The students remained at their firing point, the instructors moved over. The most common experience was for the 'new' instructor to repeat, word for word, what the 'old' instructor said, only for the student to state:
"Oh, THATS what he/she meant!"
Only the results mattered. With over 5,000 students in 9 years, only two failed shooting. One for lack of desire (I ran into the student later, who told me that they realized law enforcement was not what they wanted to do.) The other just could not "get" it, and lost their job.