Current international demands to strengthen the teaching profession have led to an increased development and use of professional content standards. The study aims to provide insight in the construct validity of content standards by researching experts' underlying assumptions and preferences when participating in a delphi method. In three rounds 21 experts judged and revised content standards about teaching students research skills. The method resulted in nine content standards with a high degree of consensus and support. A qualitative analysis of experts' comments and a Homals analysis on their preferences showed that they differ in the assumptions and preferences from which they judged the content standards. The value of consensus approaches for developing and validating content standards is discussed. (Contains 2 figures and 3 tables.)