As an educator what I feel like I do know is this:
This task cannot be quantified.
This task cannot be achieved using the same method for everyone.
This task is not measurable as a learning outcome.
But, this task is the central function of good teaching.
Measure what you want. Create tests and teach to them. Assess and assess and assess.
But, don't think what you're measuring is getting you any closer to seeing the rabbit. You can only see the duck yourself.