Art Of Problem Solving has a rating of 3 stars from 2 reviews, indicating that most customers are generally dissatisfied with their purchases. Art Of Problem Solving ranks 41st among Math sites.
My son applied for an online grader/TA job. They made him do this detailed 'assessment' which entailed hours of his time to complete. He then confidently submitted their assessment along with his application only to be rejected by telling him that they have no work available. He said that this so-called assessment involved many intricate questions that he had to provide answers to as if he were a grader/TA correcting a student's work. Wasted his time all for nothing. Not even to be told to be put on a wait list for future jobs. It certainly sounded deceptive because here they have his responses that they can very well use for their own purposes. If they are totally legitimate then they ought to not have a mandatory detailed hours and hours long sample to submit knowing full well that applicants won't be guaranteed work.
I have been using AoPS for almost two years now, and it has taught me so much more and in depth math than school ever could. Every formula is proved and the classes are very student interactive. It teaches you to problem solve and think critically.
My only two warnings would be that:
A) It's extremely hard, and no piece of cake. The site details that a child who gets straight A's in school shouldn't be sad if they get a C in an AoPS class.
B)It does not necessarily align with school standard, so be warned.
Overall amazing website!