Nicolette,
I appreciate your clarification, and applaud your obviously sincere interest in helping. You do, indeed, ask a difficult question, in part because the students may not know the answer themselves. "Is this something you can control, or is it because of your disability?" How do they know? How much of what may appear to be lack of motivation or lack of caring is, in fact, a conditioned response -- a way of protecting themselves because of past failures? If you refuse to try, you may suffer consequences for that decision, but you haven't "failed."
Perhaps a better way to approach the situation (and the student!) would be to say, "Here is what needs to be done. Here are the steps that lead to it. Here is the potential pay-off for succeeding, and here are the steps we can take if you try but are NOT successful. And here are the consequences if you choose not to even try. The choice is yours. I am more than ready to help you along the way, and we wouldn't be having this conversation if I didn't think you COULD do it (perhaps with some help). But the choice is yours." I think if you assume that every student is capable, and make the students understand that, those that are ready to accept your help will come forward. And I think that is the best you can do!
Dr. Jane Jarrow