For a long time, mathematics performance in Tanzania, especially in primary and ordinary secondary schools has been deteriorating. The performance rate in the Primary School Leaving Examinations (PSLE) in Mathematics is around 48.7% . The current study analysed the mathematics performance in Tanzanian primary schools through the lens of Candidate Items Response Analysis (CIRA) reports prepared by the National Examinations Council of Tanzania (NECTA) after the release of the PSLE results. The study was guided by three questions which were to analyse content areas students identified as the most challenging over the past decade in PSLE in Mathematics, analyse students' perceptions of the factors influencing their subpar mathematics performance in PSLE over the last decade and analyse the recommendations for enhancing students' mathematics performance in PSLE. Data were collected through document analysis by analysing CIRA reports using a document analysis schedule which consisted of all content areas assessed in each year and a list of perceived reasons for student failure. In each year the frequency of occurrence of contents and reasons for underperformance was recorded. The findings of the study indicate that most students reported Measurements, Algebra, Geometry, Statistics and Integers as the most difficult mathematics learning areas in the last decade. It was also revealed that lack of understanding of the contents, lack of logical and mathematical thinking skills, and lack of understanding of the question requirements were the factors identified by the students for causing underperformance in PSLE for Mathematics subject. Furthermore, NECTA recommends teachers should put more emphasis on teaching challenging topics, provide more mathematics practice problems to students, the government to make sure more competent teachers are employed and use of active-based and collaborative teaching methods which involve real-life situations. The study observes that most of the aforementioned factors may reflect the teacher's capacity in the contents and its respective pedagogy. Therefore, for in-service mathematics teachers, it is recommended that there is a need to strengthen in-school continuous professional development programs (known as MEWAKA) to focus on enhancing teacher's content and pedagogical knowledge in the most challenging topics. Also, for pre-service and in-service teachers, there is a need to strengthen the abilities to use activity-based learning approaches to develop student's logical and mathematical thinking skills and other relevant skills for 21st-century skills.