Art of Problem Solving

I have threatened for years now to rant about how excellent Art of Problem Solving (AoPS) is, and I guess now is the time, because E has just finished her first math class with them (Introduction to Counting and Probability), which she took over the summer. (She had previously taken their two python classes and I'd been super impressed, but I wasn't sure how representative those were.) And because her school has run out of math classes for her, she will be taking her math classes with them for... at least the next two years, and hopefully beyond that. I now kind of wish that she'd taken all her math classes ever with them (though for E in particular I greatly prioritized her socializing with other kids in person, and she's adored the math teacher she had for the last two years), and if I can possibly do so I will make this happen with A.

AoPS was started by math contest geeks, and provides math curriculum and online math classes from Prealgebra through Group Theory, which go more deeply into the curriculum and have more challenging problems than your run-of-the-mill math class, and have as a core philosophy trying to teach problem-solving skills in general rather than just how to do specific problems. (Beast Academy is their curriculum for the lower grades, which A. is enrolled in at the second/third grade level and which I've talked about before.)

( Cut for length. )