Answering various posts:

DS8 has just started one of the lowest level AoPS on-line courses. He's managing with reading the scrolling plaintext, typing responses, staying focused for the whole lesson, but only just now; I don't think he could have when younger. So "the common view is that the pace of the AOPS on-line courses are too fast for younger kids even the very gifted ones." is somewhat true depending on kid and age, at least for the "live" class. Doing weekly homework is no problem, since one is not under time pressure to respond quickly. Maybe I'll review it in a few months.

Two people mentioned "Usborne Encyclopedias". I'd never heard of them. I like the idea of children's encyclopedias. DS8 and DD5 will get interested in, and pick up and read, these types of books, as long as they are designed to be attractive to (maybe older) children. Any other suggestions along these lines?

"... $400 per child...$250 per child..." These numbers are encouraging. I don't mind paying for a well designed curriculum that saves parent and child time (less detailed planning for parent, easily compactible for child) and follows some kinds of standards. Actually I just want this for Math and ELA, and we'll improvise the rest (for elementary school). We mainly want to cover "the three Rs", and really it's writing specifically where we need well designed structured coursework. (We do not need to teach our kindergartners about ancient bloody battles like k12.com's history does.)

" For elementary age, I think I'd definitely prefer pure homeschooling (indeed, I did!)." That's what I want to hear. Unfortunately when I floated the idea with DW "Let's drop the virtual school and home school instead", her response was along the lines of "How could that even be possible?". So I've got some work to do.