Principles of scientific data accumulation and evidence-based practices are vehicles of professional enhancement. In this article, the author argues that a scientific knowledge base exists descriptive of the relationship between teachers' activities and student learning. This database appears barely recognised however, for reasons including (a) the scientific tradition may not be seen as an appropriate basis for humanistic decision making; (b) personal observations can override impersonal statistics; (c) alternative frames, such as postmodernism, may contribute towards an anti-science stance; (d) qualitative research may be viewed as representing a sampled universe; (e) educational theorising thrives upon dichotomisations which cannot be mapped against objectively-secured data; and (f) individuals are relatively unable to undertake the mental processes demanded of theory change. The author also discusses the distinction between scientific reasoning and everyday cognition, as illustrated by research findings into cognitive biases and heuristics.