Take your child back to first grade and systematically re-test his knowledge. Identify where he got lost, catch up, and then today's assignments will not be as difficult. The child is likely stuck on something that wasn't thoroughly understood in the past.
I did this for a child recently. He was in the special needs program. I looked at his homework and re-tested his math understanding. It turns out he had no solid understanding of place value and had difficulty with adding two digit numbers mentally. No wonder he was struggling. We fixed that by spending a week 30 minutes per day on just that concept, he caught up to the next roadblock, which was fractions, we fixed that, and so on.
That's expensive if you hire someone to do this, but enabling self-study through ability to backtrack would not require as much teaching skill and be more of a supervisory activity for parents.
There are entire books on how to interpret math word problems, which is really all about converting verbal expressions into mathematical symbols. If you haven't already, buy one or check one out at the library. I am building a parser that implements those books as if they were algorithms.
That's the approach I am working on. No NLP, no ML, nothing fancy like that. It will take a while, but I should be able to pull this off. This is a question about hard problems and I think it qualifies. ;)