The purpose of this explanatory sequential mixed methods study was to explore Pennsylvania K-12 public school teachers' perceptions of LMS since the onset of COVID-19. The study evaluated teachers' perception of LMS. In March 2020, schools across the United States shifted to online learning due to the pandemic. This pivot in the delivery of instruction forced many educators to acquire new instructional strategies and technologies. Consequentially, teachers were using Learning Management Systems (LMS) more due to the onset of the pandemic. With the Technology Acceptance Model (TAM) and an extension of TAM as the conceptual framework, this study explored K-12 public school teachers' perceptions of LMS. The participants of this study were K-12 public school teachers from Pennsylvania who have taught since 2019. The study took place during the 2022-2023 school year. The quantitative data was collected through a 7-point Likert Scale survey (Fathema 2013) and adapted for this study. The survey was administered to 242 participants. The qualitative data was collected through open-ended questions in the survey and through semi-structured interviews with 8 willing participants. Results indicated participants had positive perceived ease of use (PEOU) and perceived usefulness (PU) regarding the LMS they use. Teachers reported perceived strengths and weaknesses of LMS. The data showed differences between participant groups as well as no significant differences between groups. This study found statistically significant positive strong relationships between PEOU, PU, and System Quality (SQ). This study will benefit school leaders and technology companies in planning and implementing LMS to their teachers. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]