According to international studies of achievement in mathematics amongst Australian secondary school students, results have declined over time when compared with other countries. The National Assessment Program -- Literacy and Numeracy (NAPLAN) is an Australian government initiative to measure whether students have the knowledge, understanding, skills and values required for a productive and rewarding life. This paper presents a case study of a school with improved NAPLAN numeracy results to provide insights into factors that influenced student performance. The findings are structured according to themes evident in the data. The discussion explores these themes in relation to Hattie's areas of influence on success in students' learning: the school, the student, the home, the curriculum, the teacher, and the approaches to teaching. Through the analysis of data collected from a variety of stakeholders in the school, this case study highlights the importance of school-wide policies towards learning mathematics and adopting effective approaches to teaching it. These insights have implications for teachers, school leaders and systems who are working towards improving numeracy results.