It's just a thought, but on the dual cross countries have you helped him out a bit? Or maybe prompted him to hold his heading or altitude, or made other small suggestions to help?
Of course, with the average student this is the norm, and is taken the right way - ie as instruction.
Perhaps, with your student, it might be worth doing a cross-country where you just go along as 'passenger'. No review of his flight planning, no suggestions, no help with the radio, no help if he gets lost etc - to show him he can do it by himself, even if he makes mistakes, which of course he will.
You can put on a good 'show' of just enjoying the scenery and being bored!