South Asian approaches to teaching mathematics have been influential globally and are entangled with mastery approaches. This study investigates changing strategies and beliefs of Primary School teachers in England as they engage with a sustained curriculum development project. The teachers were working with a commercially available text book based scheme entitled Maths – No Problem!TM which is informed by Singapore Maths mastery approaches. The collaborative research involved seven teacher researchers in design, data collection and analysis. Data sources included classroom video and stimulated recall interviews with each of the seven teachers, plus a focus group in which the same teachers considered the role of the text books and two focus groups in which they contributed to collaborative data analysis. In lesson planning, supported by the scheme’s text books and teacher guidance, the teachers appear to focus on maths subject knowledge as they anticipate how children might take different directions in exploring the ‘anchor problem’. In classroom teaching, the teachers moved away from the use of in-class grouping and used questioning during a collaborative dialogic exploration phase of each lesson, before drawing together student solutions, supporting student journaling and introducing the text book to support reflective learning and practice.