Here are the things:
- It is impossible to know that Suzie has perfect mastery of Calculating Error. The tests we administer are little instruments that we hope will measure mastery, but all we can ever know are those measurements, never the actual thing.
- Even if our test was perfect (it wasn’t), Suzie might lose her perfect mastery after the weekend. Our data is old and outdated.
The only way I’ve seen to alleviate the pain these problems cause is to give a lot of tests and to openly acknowledge with students that what I think they know may be inaccurate.
I think it's hard for us (as teachers) to admit that our assessments don't measure student knowledge perfectly.