Worldwide, there is growing recognition of the importance of science in early childhood education. Doing science or, more formally, "science and engineering practices," is acknowledged as a critical component of early science education that requires support from the adults in children's lives. Moreover, engaging in science practices helps build the foundations for active learning, problem-solving, and school readiness. Despite increased efforts to increase science in preschool classrooms the dearth of measurement tools restricts the ability of researchers to evaluate the efficacy of these efforts. This paper evaluates a new measure to assess preschool teachers' science and engineering practices across multiple classroom contexts throughout the day. Data from 58 preschool teachers and 360 children demonstrate the reliability of the EC-SPOT in capturing teachers' practices and validity evidence in relation to an external measure of children's science knowledge as well as the sensitivity to intervention effects. The EC-SPOT critically expands the ability to capture science learning beyond typically limited formal science lessons, as it unfolds naturally and often in preschool children's everyday classroom experiences. Both for evaluating and promoting higher quality science education in preschool programmes, the field needs better ways of capturing how adults recognise and encourage young children behaving as scientists.