Teaching a mini-lesson to small groups. Teaching a lesson to the entire class. Conducting playground activities. Assisting with supervision at such extracurricular activities as sports events and assemblies, on field trips, or for study groups and study hall. Lunchroom management, hall duty, bus duty, under the supervision of the classroom teacher.
Observation can be a powerful learning experience or a waste of time.
The key to making it worthwhile is to have a specific purpose for observing that provides a necessary focus. Always note the name of the teacher you observed, the name of the school, the grade, and the subject being taught.