Excellent choice.
I first read the Wasp Factory back in the mid 90s. I think the gothic-style horror, macabre humour, social isolation and dysfunctional characters within the book would appeal to quite a few here. And if you like Iain M. Banks
and sci-fi (always M when he wrote sci-fi) then I'd recommend The Player of Games. That book is timeless and prescient in one of its main concepts; a society whose hierachy is dictated by the ability to play a game so complex it directly equates to the player's ability to manipulate the real world. Reads like it was written within the last few months, not 25 years ago.
You're an idiot.
He can barely comprehend some of the posts in his own forum. It's not surprising he can't get past the first sentence of the Wasp Factory.
Plot Spoiler:
Spoiler
I think he should persevere though. Given the relationship between Frank and his 'it was an experiment' father, and the book's revelationary ending, I think both he and Zek could emphathize with the characters. Might help his reading comprehension too.