My son is six and pretty advanced. He can probably do most of the third grade math curriculum. He can't borrow yet or carry well (those are the only two things). Standford EPGY is a good program it seems (affoardable) as is Dreambox. My son will be able to work at his own pace while his first grade class does whole group instruction. I'd like to see him advance at his own pace. What other self-guided programs are good out there. I am a math teacher and can remediate if I see he doesn't understand a particular concept. Can you help?
First of all, work with the teacher closely, for two reasons. First, you want to use your ed skills to make this process more doable for the teacher, to avoid logistic headaches that may result in bad feelings and thus negativity for your son. Second, teachers who are more on board with content will be able to help better, if need be.
Beast Academy from AoPS is another option I would recommend, in addition to those you named. It is already designed for advanced students, so it may be harder, compared to advancing to the regular 3rd grade curriculum. Check it out to see if the style matches your son's needs and desires: http://www.artofproblemsolving.com/Store/beastacademy.php