- What?
-When I want to visit them;
-How many lessons I need/want to visit;
-Why I want to observe them;
-Why I chose that course and not another one.
- Why?
-To clarify dates, timetables and to arrange a date as convenient as possible for both of us;
-To let them know how many lessons I want to visit in case I may need more than one to fully observe a certain aspect (even though that is not generally possible);
-To let them know why I need to observe a class (because of an assignment in which I have to analyse a lesson through obverving it so as to help my improve and examine my own teaching);
-To explain the reasons why I want to observe that specific course (because of the age of the students, because of their number, because of their level or simply because that was the only one available that coincided with my timetable).
The most important thing to do before observing a lesson is letting the teacher know that you are not there to test, examine or criticise their teaching but to be able to understand and analyse your own teaching through external input. We cannot see our own lessons objectively and that's why observing someone else's teaching helps you spot out different aspects to be analysed in your own teaching.