Teacher noticing of student thinking represents a key aspect of teacher expertise as it informs teachers' actions 'on the fly' during a lesson. In science and mathematics education, teacher noticing has been conceptualised as being driven by attending to and making sense of student thinking. A range of models of noticing developed in professional fields such as aviation posit that perceptual interaction is also a key driver of noticing. This paper presents an alternate, ecological model of teacher noticing that begins with the premise that teachers have limited capacity to make sense of noteworthy events mid-lesson. Multimodal data collected from a primary science and mathematics lesson, taught by the same teacher, is analysed using the ecological lens. The analysis draws research attention to aspects of teacher/classroom interaction such as attention deployment and the role that classroom environments play in facilitating mid-lesson noticing of student thinking. Differences in teacher noticing between the science and mathematics lesson can be accounted for in terms of variance in environmental structure rather than solely in terms of teacher cognition.