In the case of the assignment you're talking about, that shows the relationship between 3, 8, and 24, and reinforces it in different ways. The fact that she is getting things wrong suggests the opposite of what you thought. For one, you say it's impossible to fail, but yet she's failing the assignment. Whether it's because she's not paying attention or doesn't know the answer is irrelevant. She's getting sloppy and making mistakes. I can't think of a single job I've ever had where you can brush off an assignment because you're too good to do it.
Firstly, I didn't say it was impossible to fail...
I know what the point of the exercise was, and she completed the exercise perfectly many times before she just got bored of the simplistic repetition and total lack of challenge. We were having to force her to sit and do it over and over again and continually explain that she knows it and just has to get it out of the way.
Go back to it after a period of weeks or months and she's back to snapping through it easily and correctly.
Translated to later in her life:
There are people who can do that sort of thing for a living, they can sit in a factory and press the same button 2,000 times a day for 40 years and be relatively fine. Some can even take pride in it.
That's good, society needs people like that.
I think, given her creativity and curiosity, that would absolutely destroy her and I'll do everything I can to help her avoid that. Same goes for my son - I honestly can't see either of them being fulfilled by "a job".
That's also good - without creative thinkers that aren't satisfied with "just the same" we stagnate.
I've done that sort of job in the past, and I managed 3 weeks before I told the line manager that I'd finish the shift and never set foot on the premises again.
Now, I don't brush off assignments because I think I'm above them - but what I do is choose what I accept. This is because I've chosen to not have a boss and therefore nothing gets assigned to me. If I go to look at a job and don't want it, I can either walk away or alternatively quote a high enough price to compensate. Then I do it that once and never have to do it again if I so choose.
I get there's just sometimes things you have to do, but I (and they) need that tempered by just more. I don't enjoy doing my tax returns, but I get it done because it's a means to an end - keeping it in prepped so I can complete it once a year I can do - I couldn't do it again and again because it would bore me to tears yet some people make a career of it.
If the assignment for her was "do these three identical calculations in different orders 250 times" then I'm actually pretty happy for her to fail, because I don't think she's wired that way. I'd be equally happy with her to pass it, if it was the way she worked.
The last thing you have to realize is how many parents nowadays will complain to the teacher when their kid gets bad grades. Good for the teacher for sticking to her guns instead of caving when a parent comes in and tells them they don't how to grade. Nowadays most teachers just give the kid an A to get the parents off their back.
We don't have grades as such, we do get term reports though. Instead of being based on a one time test they're a summary of the term. For both kids they're pretty consistently "exceeds expectations" and that's nothing to do with any influence I may project onto the teachers.
In fact, it's the opposite.
If they're exceeding your expectations then raise your expectations - the ones you have now are obviously too easy for them.
If it were a test or exam I'd expect them to do quite well as that's an assessment of what has been learned and retained - the rest of the time there should be an element of challenge and of meeting that challenge.