The traffic light metaphor is an important one. Troubled schools - red light schools - should embark very cautiously on self-evaluation and only undertake that venture with a lot of external support because feedback is not always helpful, and sometimes actually quite destructive. What such school need above all is the development of self-confidence to grow better,to learn from one another and to learn from good practice elsewhere.
Amber light schools are schools with some strengths which can be built on but they also need support in what and how to go about evaluating what they do well and what they do less well.
Green light schools have above all a self-confidence to not only hear the good things but to take on board difficult messages. Such schools are eager to learn and are happy to learn from their mistakes. They value student voice; they value teacher and parent voice, and they build self-evaluation into the day-to-day life of classrooms. That is the pre-eminent criterion of a good school.