According to Bill Gates, many schools in America don't allow the principal to come watch classes without prior notice, and no more than once or twice a year. I always wondered about this, because I don't really remember how things were when I was a kid in terms of people watching the classes. The system here in Japan is drastically different:
1. The Principal visits every teacher without notice once a month. He does a review of their lesson and teaching style and gives them input afterwords.
2. There are a few days every quarter that are like an open house. Unlike the after school open house in the US, these are during school hours and last for 3 days (all these numbers vary by the area, but this is the general idea). The parents come and go as they please and can sit in on the classes.
3. There are study lessons throughout the year. One teacher will prepare a special lesson (sometimes it will be team teaching), and they present the lesson with all the other teachers watching. They all stand in the back wearing suits holding clipboards, and someone usually has a camera. Often times there will be a high level official there from the board of education, and after the lesson, which is usually after lunch on a half day, there is a long meeting to discuss the class. These lessons are sometimes for the teacher to show techniques to the other teachers, or for the other teachers to critique the main teacher. There are themes, like team teaching, or science projects. I've done quite a few of these where the theme is usually team teaching. I'm supposed to be an assistant teacher, and this is usually the only time that's true.
4. In some schools, including both of mine, there is one day a year during which the entire school is open to the public. Parents come, teachers from neighboring schools come (for 5th and 6th period, so all their kids have gone home), and anyone off the street can come in and watch the lessons or look at things the students have made in the hallways. I've never had a lesson during one of these, but I've been to a couple and it's quite an experience.
The level of accountability and the lack of reward for good teaching in the US is depressing. It's amazing that good teachers exist at all, frankly.