As a teacher, learning from the experts is highly recommended. Teaching is not something you learn by studying theories alone. Effective teaching is gained from experience as well as from proper mentorship.
Teachers, especially beginners, can’t be perfect. You can be good at classroom management and still need to improve your teaching strategies. You can be an expert in building rapport but need to work on your content. This said, you can always learn something new from others.
Observing the classes of your co-teachers will allow you to assess your own teaching style. Was the teacher highly effective in delivering the content? Was their use of visual aids perfectly executed? Was it their incorporation of other unrelated topics make the lesson more interesting? Observe the student’s reaction to the teacher’s class. Evaluate how the teacher delivers the lesson. List down the good and the bad of the class.
After the class observation, assess what techniques you can incorporate in your next classes and which methods you will likely eliminate. You may even help your co-teacher by giving him constructive feedback afterwards. Just remember that you are not observing the class to judge the teacher. You are doing it to assess their approach and strategies. Do not make any personal attacks.
Since students are dynamic vessels of learning and not structured robots, you can’t be 100% sure that what works in one class will work in yours. However, you can try and experiment. In the end, experience is still the best experience. What matters most is that during class observations, you’ve gained new insights about teaching.