OK, I think I get that, but I still think that if you have to test, you should be testing on the work the students have actually done.

Which is to say, based on the curriculum and the expected standards students should have reached by age 6, age 11 etc. This way, what is actually being tested are the teaching methods and the competence of teachers. In the UK, the tests are used to better develop child-centred methods of teaching which accommodate differing learning styles.