In this paper, I examine the nature of primary science expertise using an ethnographic and sociocultural approach and a theoretical analysis that conceptualises educational practice in terms of the resolution of dilemmas. Using data from an in-depth investigation of the perspective and practice of a single teacher, I discuss some of the "dilemmas" faced by this expert science practitioner as she tries to find the most successful ways for facilitating children's learning. The dilemmas I discuss here describe tensions around how scientific knowledge should be presented to children, how children learn science and modes of pedagogy. I show that while some of these dilemmas arise from a conflict between the teacher's own ideals and the external requirements placed upon her, others reflect important tensions within her own values and commitments. I argue that a language of dilemmas allows us to understand pedagogic practice as "dynamic" in character, as frequently involving difficult choices, in which ideals are traded off against one another. This dilemmatic perspective contrasts sharply both with those views of primary science teaching that treat it as the authoritative transmission of basic skills or facts and those that treat it as the acting out of a coherent ideology.