This reminds me a lot of my trying to learn foreign languages. I spend some time in junior high in the UK in an international school and really WANTED to learn a foreign language but I just couldn't make the vocabulary stick. I would totally frustrate the teachers & tutors. I could NOT remember what words meant even if I tried with flashcards. Totally frustrated me & the teachers.
And speed/drill arithmetic tests were never my thing either but they weren't big at school when I was a kid. (I have a BA in mathematics so it didn't hold me back.) I have the most problems with the 7 times tables and to this day I have to think to come up with 7x8. I picture on my fingers for the 9 times tables. Have you taught your son finger trick to the 9's tables? I never learned to do without, I just figured out how to do it in my head.
Seeing the multiplication tables and patterns might help. Repetition, doing lots & lots & lots of problems might help. They don't need to be easy problems, just re-using and re-using the facts over & over again. Have you had him write the times tables out in a grid, I found this helpful working with my DS even though he does memorize well.
A bit like this but I'd have him make it himself. What you want if for him to figure out the patterns for himself.
http://www.mathsisfun.com/multiplication-table-10-color.html
