Children's learning of early number bonds is a significant issue in South African schools because evidence shows that flexible and efficient (fluent and reasoned) knowledge of number bonds to 20 correlates with success at the end of primary schooling, yet the evidence is that many South African students are over-reliant on inefficient counting methods. This paper focuses on why and how treating early number bonds as scientific concepts may be the key to raising learners' attainment in these. The paper argues that teacher mediation is crucial and that mediation for learning scientific concepts has to be meaningful, relational and transcendent. This theoretical position is illustrated with examples from a dynamic assessment interview with a Grade 2 learner carried out as part of the Wits Maths Connect -- Primary project. It concludes by suggesting the implications for teacher education and professional development.