currently, if a student writes nonsense, there's a fairly significant chance that they will be caught and penalised. a human can detect nonsense in three minutes.

in contrast, i suspect algorithmic approaches can be gamed more easily because they don't adapt in the same way. they're not solving the hard ai problem; they're grading essays (currently) written for a human reviewer.

for example, what happens if a child learns an existing text by heart and then substitutes appropriate nouns and verbs to suit the context? say they learn "We hold these truths to be self-evident, that all men are created equal" and then, for an essay on their favourite pet, they hand in "We hold these kittens to be furry, that all kittens are created hungry". That's good grammar; it's got suitable references to the subject; it's clearly nonsense.