Blessedwithseven,
Unfortunately, of all the subjects, Math is something that is difficult to cram. It seems to be a skill that takes lots of time to acquire. Instead of asking, “What does he have to do to catch up?” You might want to start thinking about what you (and he) can reasonably expect to happen by the end of high school. Then, you can hold him accountable to complete as much as he can. At some point (past the basics… addition, subtraction, multiplication, and division) he might catch on and move quickly. But I wouldn’t want to push on something he might not be capable of doing. I’d hold him accountable for hard work, not necessarily to finish a whole grade level in six months (not that you’re suggesting that, but I’ve been tempted to try things like this).
My kids have had great success with mathhelp.com. I pay a yearly fee and they can go at their own pace through Pre-Algebra, Algebra, Geometry, and Algebra 2. This way when they finish one “grade” they can move on to the next without me paying for a whole new program. Also, it has videos and self-grading tests. They don’t involve me, unless they get stuck.
As a side note, I barely made it through Algebra and Geometry in high school… took Algebra three times in college, and still graduated (and earned an advanced degree).
God has a plan for your son. Keep plugging along and trust.
Jen