A nice softening of the ultimate truth. Either you know the facts or you do not and the only way to gauge whether one has absorbed any knowledge is to test it. Simple.
To think otherwise is just to place a bet. You can bet they may know it but you can't bet that they don't as that would also lean towards violating 'official policy'.
This whole pro non-zero nonsense has nothing to do with teaching children but has everything to do with teaching ideology and in addition the process is dysfunctional. If one does not get a mark for work that was assigned then it becomes as if the work was never assigned. It becomes possible that one could artificially inflate grades by only handing in assignments that they are really good at and ignore everything that they are not.