People are smart. Children can be wicked smart. Create a system, and people will find out ways to beat the system.
A grading system is established that makes no difference between a 99% and an 89.5%. You’d be surprised how many students aim for the 89.5%.
Standardized tests are supposed to be an objective measurement of aptitude. Yet tests can be studied for. The biggest correlation between test scores and another number is the affluence of a postal zip code.
But the human ability to beat systems can be harnessed. The magic comes from (and real creative labor is) devising your own system and finding ways to beat it.