Background: The co-establishment of social and sociomathematical norms in the microculture of South African classrooms and its possible effects on early number learning has largely been unexplored. Social norms are considered to be general classroom norms that are relevant in any teaching and learning space, whilst sociomathematical norms are specific to the mathematical aspects of students' working. Aim: In the midst of poor numeracy outcomes in South African schools, our interest lies in the connections between the establishment of particular norms and the affordances or constraints for learning that they provided. Part of our interest, in a context where sense-making, cooperative working and mathematical progression beyond one-by-one counting have been described as infrequent in Foundation Phase mathematics learning, was to explore whether it was possible to institute norms related to these aspects. Setting: We report on the social and sociomathematical norms established within group intervention sessions with two groups of four Grade 2 learners across 9 weeks of intervention in a suburban school which serves a historically disadvantaged learner population. Methods: The frequency of specific norm codes was used to determine the normative behaviour within groups across intervention lessons. Results: Two significant inferences are drawn from study results: a culture of co-operative working based on social norms was needed in the grouped learning space before sociomathematical norms could be foregrounded within the same space; and one particular sociomathematical norm -- 'use the structure of 10' -- was particularly important as the 'hand hold' that allowed for progression in participants' early number skills.