There are three obvious contributors. The first is that his working memory could be better. Perhaps related to that, he dislikes memorization tasks (two traits I share). Lastly, he has an uneasy relationship with time and especially with timers.
Since computer time is a positive reinforcer for him we tried some computer based math exercises. First I went to the web, where I was again reminded of an old unsolved business problem. We have yet to figure out a way to deliver quality web based software solutions to this kind of niche market. It's not a technology problem, it's a business problem.
The best web solution I could find was Math Playground, and that required digging through heavily ad surrounded sites, sensory overload sites that were annoying even to a non-Asperger's person, dozens of me-too sites, spam sites, suspicious domains, and so on. In other words, lots of junk or marketing efforts.
Once upon a time I might have tried finding educational software for OS X or even (further back) Windows, but that market hasn't just died, it's died a thousand deaths. Another market failure, one perhaps related to the web failure. (Hint, no copy protection, niche market, high cost of entry, high cost of marketing, etc.)
Of course there's also the Wii, but those apps tend to be very expensive (Nintendo's cut), heavy on the entertainment, and rarely focal enough for my needs.
So I skipped from the web to the astoundingly successful Apple (iPhone/iTouch) App Store.
There I downloaded five Math Drill apps. Some cost money, some were free. The ones that cost money were all less than $3 so, as far as I was concerned, they were as good as free. There are lots more Math Drill apps on the site, but these all had some history of use and reasonable ratings. The ones that cost money had very good ratings. (Hint, always read the negative reviews first, and look for the rational critics.)
- Mental Maths: This one's from a German math prof I think. Must be German, since the "level 2" multiplication was somewhat challenging even for me, and there are four levels of difficulty! The key feature is one can adust both time limits and difficutly, and store statistics by name (so different children can be tracked). (The app needs a way to clear the statistics by the way!) During the exercise one gradually uncovers a pleasant animal image, which was just right for B2A.
- Math Cards: Simple, this one shows multiple choice answers and tracks one's score. I prefer having my son enter the numbers, so it's not quite enough.
- Math Drill Lite and Math Drill: The Lite version is free, but you can't track settings per child/student. For that you need Math Drill ($2). So try the Lite version first. In a few minutes testing I was happy enough with the Lite version that I upgraded. You can create many students (I created four - 3 kids and me). The active student name displays prominently on the first screen, a feature Mental Maths could emulate. The UI is attractive, there are lots of student-specific settings, and there's an optional number line.
- Mighty Math Lite: Ad supported, and I find them extremely annoying. It's "free". I really don't like most free software, and this one was no exception. Avoid it.
- Flash Cards: Again, multiple choice, fairly comparable to Math Cards. Free I think.
Apple's on to something here. I think the combination of the App Store distribution channel and the iPhone/iTouch platform are going to take niche software, including special needs software, in a very interesting direction.