How teachers need to know the content they are teaching in order to create opportunities

1) How might teachers need to know the content they are teaching in order to create opportunities for their students that help them (the students) understand important subject specific ideas? Such opportunities to learn may be activities, experiments, excursions, readings, discussions, etc.) 2) Describe the three most important characteristics (in your opinion) of a "good" assessment. Why are these characteristics so important? Support your arguments with evidence.