I don’t have time to track down the link at the moment, but sometimes struggling with math facts can be a symptom of dyslexia (which is actually NOT a learning disability or even medical condition, but simply a result of one hemisphere of the brain being larger than the other – it can mean giftedness in music, sports, art, and building – tactile things).
I’m JUST learning about this, as it runs in my family and I have a dd that might have a few sypmtoms. I “accidentally” read an article about it – it can also result in poor spelling – (that’s what I like to blame!) often students are quite bright, but may hit a wall with reading around 3rd grade and struggle with memorizing math facts, yet solve math equations quite well!
Sorry, that doesn’t help him memorize his math facts, but just thought I’d mention it so you can keep it at the back of your mind in case whatever suggestions you get don’t seem to be working.