Children are innately mathematical and explore mathematical concepts through play. However, educator beliefs about mathematics can impact the inclusion of mathematics in early childhood education (ECE). Recent research has suggested that spatial reasoning is a key concept which forms the foundations of mathematics learning. The theoretical argument underpinning this research is that young children benefit from intentional teaching specifically focused on supporting the development of children's spatial reasoning skills during play. This mixed-methods research project investigated the effects of the implementation of a suite of play-based, spatial reasoning activities on educators' teaching practices--including observations, assessment and evidence-based planning--and educator beliefs about mathematics in ECE. Twenty-seven participants were educators from 15 early childhood centres for children age 3-5 years, based within culturally and socio-economically diverse populations. Participant qualifications included diplomas, graduate and postgraduate degrees in early childhood and primary education, with teaching experience ranging from 6 months to 35 years. The investigations found reciprocal influences between the three key areas of the research project which included: the implementation of the activities by educators, educator beliefs about mathematics, spatial reasoning and mathematics teaching practice. The findings have implications for further research and curriculum design and practice. These include the need for research methodologies which contribute to sustained professional learning outcomes and the uptake of research findings in practice, play-based spatial reasoning assessment strategies and the contribution of a focus on spatial reasoning to early childhood curricula.