After the outbreak of COVID 19, 192 countries took immediate measures by closing school aiming to mitigate the spread. Ethiopian is one of them. During the school closures, Ethiopian Ministry of education along with regional educational bureau was providing distance education. Despite the attempts to keep on formal education; the accessibility, effectiveness, and equity were challenging. Considering that studies in Ethiopia have been conducted by international organization. But the studies miss two important things. First fails to examine the challenge and gap in high school education during school closure times. Second, the impact of COVID on students' math performance has not been well studied. But studies done in European and some African countries shows that there are significant challenges for high school students. High school dropouts, significant educational loss, and mental health problems were among the challenges. In terms of math, there has been a significant decline in math performance. Taking the above facts into account, this thesis examines the impact of COVID on a student's academic performance, taking Grade 12 students at Millennium High School. An exploratory sequential mixed research design is used for studying the impact. In the first phase, qualitative data concerning the impact of COVID on student performance is collected from teachers and the school dean using semi-structured interviews. The collected data from the interview is analyzed using thematic analysis. The result has been used to prepare the questionariesâ€™ that are going to be used to collect data for the quantitative phase. The quantitative phase was studied alone to assess the extent of the impact. Finally, the results of the two phases are integrated and studied. From the study inaccessibility of education, the difficulty of homeschooling, poor assessment, reduction of class hours, and poor learning took was the major theme identified that impacted the academic performance of the student. Concerning math besides the above finding of the nature and difficulty of the subject math by its self-taken identified as a good contributing factor behind the poor academic performance, of students shows in the subject.