Read and write what? Should an 8-year-old be reading chapter books? If so, which ones? Back up your claim with research.
What level of algebra should a child of 8 be doing, and on what theory or research do you base your answer?
Aside from your belief, on what do you base your theory that "every 12 year old should be learning Calculus?" EVERY 12 year old?
I couched my argument in terms of "you can't say." I stand corrected. You can say it all day long. It will be the same giant turd the state has plopped in our public schools, but you sure can say it.
> What level of algebra should a child of 8 be doing, and on what theory or research do you base your answer?
On the theory that it's far easier to learn the non-intuitive rules before your brain loses the plasticity of childhood (i.e. the thing that makes kids such excellent learners); the jewish tradition of bar-mitzvah is held at 13, and at such point "they become accountable for their actions." (See wiki) -- so there's a whole culture that has the "adult-bar" (more accurately accountability-bar) placed fairly low. [Actually more than just the one, but it serves as a good example.]
As I said previously, you implicitly have to have all the skills and knowledge to function as an adult before you reach your adult age -- I believe that calculus should be one of those, as should: logic (informal is fine), philosophy (at least the basics), theology (your answer to "who/what is God" deeply impacts every facet of life), cooking (at least enough that you could make something edible from the common contents of a refrigerator), cleaning (you should at least know how to clean up [doing is another matter, I should know I'm a bachelor]), accounting [really 'record-keeping' w/ a little basic arithmetic].
Basically everything one needs to be a functioning adult human.