In that case I would certainly start with marshmallow math. Go through it and see where your son is. Then go from there. Check out the site
www.ixl.com. They have an amazing list of the scope/content that meets the standards for each grade. I use the site to assess my sons abilities. And it helps me see where he has a deficiency so that we can work on that. You can access the grade content for free and do a few test questions for free daily. Or you could sign up for a $10 monthly fee.
What I do is sign up for a month and have my son work through a grade level. Then I suspend subscription until he is ready to complete another grade level.
There are a lot of full curriculum math programs, all quite different. It is near impossible to compare Jones Genius, Singapore Math, Saxon Math, Horizons Math, Math Mammoth, Miquon, MEP, Jump Math and Right Start.
Now those are just a few of the more popular programs. I have read good reviews on all of them.
But it all comes down to what kind of learner your son is, and what kind of teacher you are. Price is also a big contributing factor.