Is he getting good marks for the homework, but then poor marks for the tests? I'm a bit confused because you describe him as "academically challenged" but also as a "poor test taker" which I think of as two very different things. I think he'll probably need quite different help depending on whether he performs well in everything except tests, or whether he has more general academic problems. Maybe the school would be able to refer him for some detailed testing - hopefully done in a relaxed enough way that the tester would be able to get a full picture - that might show where he has bottlenecks that you might be able to help him get round?
