The shift from additive to multiplicative thinking is challenging for students. A professional learning program was developed that focused on an identified area of need by teachers, namely multiplicative thinking. Program content focused on concepts underpinning multiplicative thinking, pedagogical approaches, challenging tasks, and application to classroom practice. It was delivered via six 90-min modules in 13 participating schools across terms 2-4, as part of regular after school professional learning. Whilst all staff participated, the research focus was year 3-4 teachers. Students' historical data were collected across four years (2016-2019) to determine mean growth over time, in participating and non-participating schools. National Assessment Program Literacy and Numeracy (NAPLAN) and Mathematics Assessment Interview (MAI) data were used to determine the impact of the learning, as both assessments are administered annually. Analysis of year 4 students' longitudinal data showed greater mean growth in student learning over a 2-year period in schools involved in the learning and additional in-class coaching support, than students in non-participating schools. Our findings showed that targeted school-based professional learning, with in-class support from a knowledgeable other, leads to teachers' improved understanding of multiplicative thinking and subsequent pedagogical content knowledge to support student learning.