Ethiopia has established the national learning assessment system since 2000. However, it rnnever participated in any regional or large-scale international assessment, though, rnplanned to join it as of the Fifth Education Sector Development Program. The purpose of rnthis study is, therefore, to assess grade eight students' mathematics achievement through rnthe lens of Trends International Mathematics and Science Study (TIMSS). This was a rnquantitative study, in which the released TIMSS mathematics achievement test items and rncontext questionnaires were employed. The participants were 2,120 students selected rnthrough two-stage cluster sampling techniques from 53 schools of the three regions (Addis rnAbaba, Benishangul Gumuz, and Oromia) and school principals of the respective sample rnschools. Descriptive and inferential statistics were used to summarize the findings and rngeneralize about a population from the samples. The results indicated that the overall rnachievements of studentsâ€™ in mathematics were about 32% and 404 points in the raw and rnscale scores respectively. The mean scale score for Ethiopian students was significantly rnbetter than the mean score of four African countries that participated in TIMSS study in rn2011 but lower than the international mean score (p < 0.05). There was a statistically rnsignificant achievement mean difference across gender and school location, in favour of rnboys and rural schools at p < 0.05. The highest regional average achievement was rnobserved in Oromia and the lowest in Benshagul Gumuz, while Addis Ababa was in between. There was no statistically significant difference observed between the rnachievements of Ethiopian students' in this study and National Learning Assessment (NLA) rnstudy in 2016, with the mean scale scores of 302.05 and 300.36 respectively (p < 0.05). rnThe main significant factors that affect the achievement of students were: gender, school rnlocation family SES, students' attitude to school and mathematics, instructional language, rnschool feeding, school emphasis on academic success, and principals' qualification. In rngeneral, the achievement of students in mathematics was found below the expected national rnand international standards. Therefore, policy-makers and concerned stakeholders should rngive special attention to enhance the achievement of students in mathematics, particularly rnfor those disadvantaged low achieving groups. Finally, to participate in International rnLarge-scale Assessment (ILSAs) and make the right decision, further studies should be rnconducted countrywide as this study has left with unanswered questions