ETA - Is there a children's hospital in your area? Check with them. They can at least give you good advice. Also, check out Dyslexia sites.
Dyslexia is a far different testing than the rest. You need an actual expert at dyslexia testing to do this. Research that more closely. I wouldn't want just an overall approach done by someone without that specific expertise.
I think you are very wise not to start meds after 5 minutes of assessment. I HATE doctors like that. Shame on her.
Use any medium to help him with the reading. Make sure that he's reading stuff he likes. My younger son had incentive to try because he wanted to read about Pokemon. Now, that was a long time ago, but it's an example. Even Captain Underpants (usually 2nd grade fare, rolling my eyes!) will grab a boy.
Do you go to the library with him in the summertime? You should take him every day. Let him read all kinds of "junk" - car stuff, Yu-gi-oh, sports, anything that he likes. Then check out a series of books with exciting stories that you read aloud to him. The librarian can point you toward some great stories. I recommend that you start reading Harry Potter with him. It will take a long time, but it's a great mother/child activity.
I do think that the testing will reveal one or more learning disabilities. A speech/language therapist might be very helpful, in case it's a language issue. Sometimes it's not really about a lack of attention - it's about not making sense of what's in front of you. A child just won't stick with something when they can't make sense of it.
I also want to urge you to find out through this testing (make sure you mention it) that they determine what mode of learning works for him. What KIND of learner is he? This way, you can get him help that works. With the results of the testing, set up an IEP with the school to help him. It will make a big difference.
You are your child's advocate like no other. You can do this!!
Dawn