This article examines prospective elementary teachers’ difficulties and growth with language for defining the whole. Thirty-three prospective teachers participated in a semester-long classroom teaching experiment conducted in a content course focusing on mathematics for teaching elementary school. The results of this study indicate that three mathematical ideas became taken-as-shared as prospective elementary teachers developed an understanding of language use for defining the whole. The first was that fractional solutions depend on a group or whole. The second included defining an of what. The third was developing language in terms of what the denominator represents.