Work on his English then - that's where boys fail (quite often).
I mean it is hard for them to write well if they are good at Maths.
He needs a lot
of practice to get to the point where he will begin enjoying it.
For some it may be something as trivial as speed they write with.
However in my opinion Comprehension should be treated as a very logical exercise, as you may not know meaning of words and still manage to answer questions.
It comes with confidence.
And as a parent it is much easier to mark Maths and VR - but only teacher or tutor can mark their English essays/Comp.
At times we were doing just one subject in depth.
My DD is very grateful to her tutor as he helped her to get confidence - so listen to your tutor, don't project your worries onto your son and enjoy teaching him.
It does bring us closer to our kids