Most rigorous HS math curriculum

[rbc54]

Hi. I'm looking for a set of textbooks for high school math (mainly algebra and precalculus) that is very rigorous and challenging. I have looked at AoPS (which I've read is considered to be the most challenging), and even have their books, but I wanted to see if there was something even a step above. I've heard mentions of Singapore, Dolciani, Cambridge A-level books, Indian NCERT books (http://ncert.nic.in/textbook/textbook.htm) etc, but I'm not sure how they compare in difficulty.

My son is rather interested in math and I'm just looking for something that's enough to challenge him. For reference, he started working through Dummit and Foote this summer just for enrichment and is around the Sylow theorems at the moment.

Thanks.

[....]

Singapore and Dolciani are going to be a step down from Art of Problem Solving (IMO).  I think the Cambridge books will be, too - but that's just a guess.    

If you're at that point where AOPS is not enough, I would start looking at college math courses - either texts or online courses.  I have mostly fine arts kids (rolling my eyes, because they would cry and attack me with their paintbrushes if I found them online math enrichment - lol), so I'm not super-knowledgeable, but it seems like MIT and Harvard both had open-source online courses?  I know there is Coursera, also.   

Here's a list I found on MIT's website:  https://ocw.mit.edu/courses/find-by-topic/#cat=mathematics

I stumbled upon some courses on Harvard's open source site, too, but you would have to do some googling, because their website was more complicated than MIT's.

There's also some higher math on Khan Academy...

Not exactly AOPs, but Life of Fred has some unusual math courses for high school.  My oldest is working through the Statistics textbook right now and we both really like it.  He has Linear Algebra, Real Analysis, a book that covers Set Theory/Topology/Abstract Arithmetic...  If we had time, I would work through the Linear Algebra book with dd17, but she is graduating in December.