Hi Timothy, Back up plans can be life savers. As we become more technological with media delivery there is a greater chance delays or unavailable resources might occur. Electrical shortages or power outages complicate everything. Moving to another room that is unfamiliar. Mechanical teaching aids that fail to function. Running out of some needed substance (gas, chemical, liquid), or supply item. These few mentioned Murphy's have happened with me and in most cases it was not because I didn't prepare beforehand - things just happen. I recommend back up plans that are low tech, related to the general topic, can be pulled off the shelf or implemmented with little notice, and contribute to a meaningful instructional session so student feel the teacher is not just filling time. Review of recent lessons, class, individual or group discussions, or practice worksheets are a couple of examples that have worked effectively for me in the past. Barry Westling