Have you talked to your school district about options for pre-algebra yet? I would start there for two reasons - one, you want to have your ds study a course that the district will recognize as an actual course rather than enrichment (so he can move on rather than having to take pre-algebra over again, also so he can prove mastery) and second, because I'm guessing there's a chance your district might have an option in place already that he could use for pre-algebra. Granted, it's only a guess, but for instance, our district has it's own online pre-algebra course - used primarily by 6th graders taking pre-algebra that isn't offered at their elementary school.
I would suspect that your district's gifted department would be familiar with either EPGY or CTY and would consider granting credit for courses through one or both.
polarbear
