Abstract: This study investigated the impact of algebra background on upper secondary students’ mathematics performance. The researcher used nonprobability sampling methods, specifically convenience sampling techniques. The convenience sampling technique was used to select participants who were easily accessible and willing to participate. The sample size consisted of 197 students from three schools of general education in Ruhango District and five teachers teaching mathematics. The pre-test and post-test were carefully designed and tested to ensure that they were reliable and valid. The pre-test and post-test were administered to measure the participants’ algebra background and performance in mathematics. The pre-test included questions on algebraic concepts, while the post-test included questions on a range of mathematical topics. The questionnaires were used to collect data from teachers assessing students’ algebra background. Document analysis looked at documents such as textbooks, curriculum materials, and assessments to gain a better understanding of the algebra and mathematics content covered in the upper secondary schools in Ruhango District. The IMB SPSS software was used to analyse the data that was collected. The study found that there is a strong correlation between students’ proficiency in algebra and their overall mathematical ability. As a result, the study recommends that educators, students, and researchers should place a greater emphasis on assessing children’s mathematical backgrounds, with a particular focus on their familiarity with algebra. The study also provides suggestions for improving both arithmetic proficiency and algebra knowledge.