This paper is methodologically based, addressing the study of mathematics teaching by linking micro- and macro-perspectives. Considering "teaching as activity", it uses "Activity Theory" and, in particular, the "Expanded Mediational Triangle" (EMT) to consider the role of the broader social frame in which classroom teaching is situated. Theoretical and methodological approaches are illustrated through episodes from a study of the mathematics teaching and learning in a Year-10 class in a UK secondary school where students were considered as "lower achievers" in their year group. We show how a number of questions about mathematics teaching and learning emerging from microanalysis were investigated by the use of the EMT. This framework provided a way to address complexity in the activity of teaching and its development based on recognition of central social factors in mathematics teaching-learning.