This qualitative study aims to understand further the lived experiences of high school mathematics teachers who underwent a sudden transformation into emergency remote teaching due to the COVID-19 pandemic. The study used a qualitative approach, specifically an interpretative phenomenological analysis. Emergency remote teaching has been a new phenomenon that has presented itself worldwide. This study used two methods for data collection. The first method used was the general participant demographic information survey, a demographic tool collection instrument created by the researcher. The second method for data collection included responses from one-on-one semi-structured interviews. A total of 13 participants completed the data collection process and were included in the data set for this study. The results of the data analysis processes revealed seven emergent themes. These themes were technology training, low student engagement, availability of technology, providing services, co-worker support, low student achievement, and preparation for future emergency remote teaching. Findings suggest that ERT is sustainable as a method of effective education should a crisis occur. However, the findings show that there are still significant challenges in improving the implementation of ERT in a K-12 setting. Finally, the results of this study show that educational organizations need to realize that the time to prepare for ERT is before the crisis occurs. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]