Delivering common assessments and view those results across teachers and schools is a great benefit of using Naiku. When creating and administering common assessments, you want to ensure that the same assessment is being administered to students. That is, you don't want the the test (and the items on that test) to have been edited or changed by anyone. This ensures that it is indeed a common assessment.
To make a Naiku assessment a common assessment, you need to "prevent edits" on that assessment. To prevent an assessment from being edited, select the "Prevent Edit" checkbox when creating a new assessment. When you prevent edits, teachers who assign that assessment to their classes cannot change or edit the assessment in anyway. Only the creator of that assessment can edit that assessment.