Why? What compelling interest of the State overrides the individual right that makes it necessary to test math competency or astronomical knowledge? Does knowledge of math impart intelligence? Honor? Morality? Loyalty to family, community or country? Does it insure happiness?
...or that the Earth revolves around the Sun.
Sherlock Holmes addressed this very question (and obviously it was the thought of Sir Arthur Conan Doyle who was not unsuccessful or considered a dolt). Holmes said "I am not interested to know that the Earth revolves around the Sun. I don't need to know such things. The knowledge of it has no practical use to me."
An awful lot of people here seem to think that education (which is stretching the limits of logic and common sense when applied to government schooling) is necessary to the acquistion of intelligence, happiness and productivity. That's a load of manure big enough to fertilize eastern Montana! What is truly disturbing though is the recurrent idea that 'society' has some right to standardize the fit and form of the individuals that make it up. What's worse is the idea that the State ought to use its power and force individuals to conform to this societal ideal. Seig heil (Hail welfare), Comrades!
Abraham Lincoln and George Washington Carver can thank their lucky stars they were born way back when.