Answer:
Public testing is a way that the school districts can rate the learning progress their students are learning, how ever if the test in is for state testing it is to compare the state testing scores against the other states.
However the tests are not technically valid because depending upon your mood depends upon how well you do on a test. So if your having a bad day and your doing one of these tests, you probably won't do as well than if you were happy and doing it.
Hope this helps!