Teachers Observing Teachers: A Professional Development Tool for Every School

For me, these are the most important points:

The most positive benefit of teacher-to-teacher observation is that it makes teaching a public rather than a private act.

Professional development should be job-embedded.
 
If done well, it is carried out in a real, practical, immediately relevant situation.

Rather than leaving school to travel to a staff development building to hear non-teachers talk about something that they learned from someone else, I  think we should stay at school and learn from one another.