DIAGNOSTIC PRINCIPLE

The mark is the signal. The diagnostic task is to find where the route first becomes unreliable.

A conversation, a school paper, the student’s working, a short probe and live observation can all provide evidence. They are not competing first steps, and every student does not need the same diagnostic test. We use the smallest amount of evidence needed to distinguish likely causes, then verify the diagnosis by repairing the suspected weak link and checking whether later performance changes.