There are 2 perspectives regarding questions, the ones students ask and the ones we ask.
In this post I am focusing on the questions we ask.

Asking the right question is half the answer

“Why can you get A’s in math and not in history?
It must be because you aren’t trying hard enough.”

“Why can you sit for hours reading books you’ve taken out, and yet can’t crack open your science book?
It must be because you are irresponsible.”

These kinds of questions are judgemental.
While it may seem like you have the answer, the opposite is true.
By providing a theoretical but judgemental answer, you have actually closed yourself off from the true answer.
The right way to ask a question is with an attitude of curiosity and room for an answer.

Here’s what the right question sounds like,
“I see you are smart/capable/intelligent, you get A’s in math.
What is it about history that is difficult?”

“I see you enjoy reading.
What is it about science that you seem to struggle with doing the reading?”

Expecting a child to answer requires that
a) s/he feel you are curious and looking to help, rather than judgemental and looking to fix
b) is even able to identify the problem. If someone has a physiological problem for a long time, this is their normal and they don’t know they can see or hear better or write more quickly. The only way to get those answers is to have an appropriate professional asses the various physiological functions needed for the task in question.

Change “Why (are you doing this)?” into “What (is going on for you)?”