On the other hand, his computer skills are a relative strength now. In the future they'll be the foundation for the cognitive aides he'll live with for the rest of his life. So I want to build those skills.
He's long had his own user account on our MacBook, with OpenDNS filtering and Parental Controls logging. He can use that with close supervision, but it's not appropriate for lightly supervised homework.
So I've created a new "homework" account that's really locked down ...
Be the Best You can Be: A simple English wikipedia
... I subsequently configured a user account on the family MacBook restricted through Parental Controls to Tar Heel Reader and Simple Wikipedia. This is effectively a homework account, in addition to the web readers it includes Calculator, Grapher, Dictionary/Thesaurus, Google Earth, AppleWorks and the weather, time and calendar widgets...
The homework account is useable with much less supervision than a standard account. In time I might make this available to all the children without time restrictions.
 I do too, but I'd hope right off if I faced the consequences he gets. The inability to adjust behavior to consequences is one of the gravest disabilities for many "explosive" children. That's why the fights we have are also valuable. If he can learn to manage the timed computer intervals, then he will have acquired a critical skill. Lately he's done quite well with an iPhone Timer running next to him. He likes the look of it, and the way the numbers move down. Even the alarm sound works. With this setup, and years of struggle, he's doing pretty well. Timer skills are key for him, so this is a double win.