[halspero]

Well physical quantities like length, time can be measured. Also fungible goods like wheat, oil. But knowledge is differentiated, non-homogenous and subject-specific. So it isn't measurable. Memorised facts like spellings, historical dates and common types of exam questions can be counted but these aren't useful in themselves. Knowledge is information that can do things.

[throwaway729]

I feel like knowledge is one of those "I know it with I see it" type things. It can be assessed, but not systematically via a multiple choice standardized test. Which puts a lot of trust in the judgement of teachers.

Not exactly a politically viable solution in America.

[halspero]

"I know it with I see it". Yes indeed. One has to interact with a person to know that he knows stuff.