While we might be able to calculate the percent of points students earn on an assignment, it is difficult to conclude that we know confidently that a student who scores 90% really knows 1% more of the total than the student who scored 89%.
Perhaps the most ridiculous myth that we (and this is a collective we that comprises educators, curriculum experts, employers, politicians, and book authors) believe is that we know what our students will need to know in the future.
Field trips, well-stocked libraries, and time to read and explore unfamiliar topics are all strategies for enhancing and extending our students' foundational knowledge.
The "gold standard" of science may be randomized double-blind experiments, but just because ethics preclude you from doing it do not mean what you are doing is not science. Of course, jut because you are does not mean you are doing science.
In political processes, participants are not bound to evidence and reason in the same manner as scientists and scholars; so, any decision can be justified. Keep that in mind when you hear folks talk about their "data."
Even those educators who claim to be unaffected by psychology or learning theory (in my experience a large majority of teachers eschew theory), their teaching is grounded in someone’s concepts of psychology and how human brains function.
Campbell's Law: "The more any quantitative social indicator is used for social decision-making, the more subject it will be to corruption pressures and the more apt it will be to distort and corrupt the social processes it is intended to monitor" is particularly true in education.
"I am, somehow, less interested in the weight and convolutions of Einstein’s brain than in the near certainty that people of equal talent have lived and died in cotton fields and sweatshops." -Stephen Jay Gould