In terms of remediation, whatever you can do to help him build up a little more automaticity for math facts will probably pay off down the line, in higher math. But he may or may not be able to get those numbers up much more. Kids with this profile need tons of repetition to attain something approaching normal automaticity.
Whether or not he can improve his speed on times tables, you may want to ask for accommodations in school to include extra time, and using the computer for as much writing as possible, so that he can use spellcheck, word prediction software, thesaurus look up (because there are probably words he knows how to use, and recognizes in print, but can't spell well enough even to look up in the dictionary), and typed responses.
