Learning to Be Flexible
Change is ever-present in education, so it is important that you keep this idea of flexibility in all of your lesson plans. Some courses truly need periods of time without interruption so that important assignments, like science experiments and timed tests, can be completed. Therefore, these assignments must be given on days when you have the least chance of interruption. In other words, do not assign a time-imperative lab on a day when a planned fire alarm is scheduled to occur.
However, be aware that despite all the planning, you will eventually have to face the inevitable and scrap a great lesson because the time was stolen by an unexpected event. In the end, it is important to have a flexible attitude at all times, if for nothing more than your own health.