Hello!
If you explain to the student that their progress is below that of an average student ...
Never ever tell a student that he is "bad", "below standard" or anything negative at all. This will slow him/her down even more, because it makes them nervous and afraid of making even more mistakes. If your FTO requires you to fill in grade sheets, hide them from the "bad" students. Or "forget" to bring them, when they ask about it. Or "forget" to fill them in (thats what I do, followed by a phone call to the instructor who is going to fly next with this student in which I tell him what to look for).
Instead, highlight their strengths as much as you can ("
I like the way you prepare your flights" or "
You are really our only student who is always here on time" if no other positive remark about the flying can be made), followed by one
but (and really only one but per flight!) adressing a weakness. Give them homework to do to help them get better, like doing navigation excercises on their PC simulator or memorising their checkpoints along the route.
For me, the real challenge of instructing is making good pilots out of not-perfectly-talented people. Flying with good students is just boring in comparison
Over the years I have only had one hopeless case. A real gentleman, recently retired automotive executive, who used to travel on business jets at work and who wanted to finally fulfill a dream of his youth by learning to fly. All the instructors of our school took their chance with him, but it just didn't work out. After nearly 100 flying hours (money didn't matter to him), he realised that it would not lead anywhere, and begged the school owner to let him do one single solo pattern. Just one. But no instructor (including the owner and the CFI) had the courage to sign for it. A real pity, as he was (is?) such a nice man. To me, failure at instructing feels much worse than making my own mistakes.
Greetings, Max