Foxmoth - it doesn't sound like they have an issue with not 'clicking', just with the student not putting the work in to pass the ground exams.
It sounds like the OP has put a lot of effort into this student, which should be applauded, sadly the student needs a certain amount of self-motivation and discipline/will-power/determination, call it what you will.
Perhaps he just doesn't want it enough?
You can drag a horse to water, but you can't make it drink.