My son used IXL quite a bit early on and it was a very good tool for him to increase his knowledge. The downside is you only get instruction on something new once you miss the problem. Not an ideal way to learn but it works pretty well.
He finally moved to EPGY and it is good up until Geometry which is very poor due to their Proof Environment. EPGY is a good program and is fine as long as there are no issues. They have staffing/personnel issues so if your son has a problem or there is a technological issue it gets real bad real quick. The Proof Environment was his first and only issue and unfortunately they could never sort it out so we moved to Art of Problem Solving.
One thing to consider is if your son is smart and disciplined he can cover a lot of material in a short time and you will end up many grade levels ahead. Be sure to consider how the school will handle this as he progresses.
