This study sought to assess the reading fluency of learners of a particular primary school in Serenje District since it was not known how fluent learners of a selected primary school were in reading and what contextual factors contributed to the reading fluency of the learners. Specifically, the objectives were: first, to assess grade 5 learners’ reading fluency in English at a selected primary school in Serenje District and secondly, to explore factors affecting grade 5 learners’ acquisition of reading fluency in English. The study employed a concurrent mixed methods design in which both qualitative and quantitative approaches were integrated. In total, the study had 50 Grade 5 pupils (21 females and 29 males), 2 Grade 5 class teachers and 2 senior teachers for upper primary section at a selected school in Serenje District. The selected primary school was randomly sampled from the top five ranked schools in Ibolelo Zone of Serenje district. In this study, the researcher involved Grade 5 class teachers and senior teachers in upper primary in one-to-one interviews using semi-structured interviews. Grade 5 pupils’ reading fluency was assessed using a standardised reading fluency test. The main findings of the study revealed that about 62 percent of grade 5 learners at the selected primary school were reading at frustration level in English. Additionally, the average Words Per Minute (WPM) was 44, the average Words Correct Per Minute (WCPM) was at 38, the average prosody score was 7 out of 16 points, average written comprehension score of 1 out of 5 marks. Further, the following factors positively affected grade 5 learners’ acquisition of reading fluency in English: Reading practice, availability of teaching materials, differentiation in teaching, teacher quality, oral English proficiency, teacher-pupil rapport and methodology factors. Additionally, the following factors negatively affected grade 5 learners’ acquisition of reading fluency in English: Limited instructional time, poor literacy backgrounds of learners, lack of teaching materials/resources, poor teacher quality, poor pupil quality, lack of parental support and policy. The study concluded that poor performance of grade 5 learners in reading fluency in English could be explained by a number of negative factors. The study recommends that the Ministry of Education should consider explicitly infusing reading fluency content in the Teacher Education curriculum for pre-service teachers so that teachers are prepared to teach reading fluency once deployed in primary schools.