My son is finishing the AoPS Intro to Number Theory book. He is self-studying as the timing of the online course is not convenient and I am not sure necessary. There have been a few chapters he breezed through and others have been quite challenging.
This is his second AoPS course (first was Intro to Programming) and I like their material.
He did EPGY for Pre-Algebra, Algebra and Intermediate Algebra. I think AoPS may be a better course as the questions seem more challenging.
I have also purchased AoPS Intro to Geometry and AoPS Counting and Probability that he will do next. EPGY's Geometry course was not very good.
