This paper proposes the use of a key biological concept--broad classification--to teach the provisional and contested nature of science in school biology curricula. It also examines existing curriculum-related factors which might pose obstacles to implementing such a change. An investigation in South Africa highlights the problems regarding biological classification at the kingdom level of 50 biology students entering one university. Using interviews, questionnaires and document analysis, factors thought to affect learners' ideas were investigated, including the understanding of the changing and contested nature of scientific knowledge of a range of biology educators (35 teachers, 33 university academics, five teacher educators, four curriculum developers and two textbook authors). The students lacked knowledge of the concept of a biological kingdom, and showed archaic thinking about the number of kingdoms. Many of the teachers held similar views, used outmoded classification systems in their teaching, and were unaware of the history of changes in biological systems. A review of two relevant syllabi and five textbooks revealed insufficient, inaccurate, inconsistent and/or contradictory information about biological classification systems and how they change with time. Three potential problems associated with curriculum innovation are discussed. (Contains 5 figures and 1 table.)