I guess the easy way to decide when to graduate a kid is by checking what the requirements for the local school system are and seeing if you've done it. Also I have kind of thought of what I had when I graduated as well. But my goals and school's goals are not necessarily the same. And I'm not sure I could mark off my goals and say "There, now we've done it." I tell my kids that they should always be learning, always be doing something. Some moms when I told them S. was thinking she wanted to go ahead and graduate kind of had a "Well, too bad." kind of answer to it. And if I thought she was just trying to get out of work, I probably would feel that way too. (And truth to tell, it would be no heartbreak to her to quit science and math.) But if she were to graduate I would expect her to fill her time with other useful things like more concentrating on learning to manage the house, helping teach the younger kids, cooking, gardening, learning the bookkeeping for Rand, and she would still take her piano and voice lessons. That's a bit to keep her busy. And she always reads anything I toss her way. She can't keep her nose out of a book.
Another thought I had was just to assign her every book I could think of that I wanted her to read in the next couple years and let her be done when she was done. If it took her a year, fine, if not, fine too.
I guess it doesn't really matter because she decided she didn't want to. She was afraid she would look like she was trying to jump the gun or something. But I think I will see if I can come up with that book list anyway. It's good for me to think about.