Research undertaken with graduate trainee science teachers into their conceptions relating to the evaporation and boiling of liquids and the escape of gases from solution. It is clear that, even after many years of science study, conventional scientific views are not always strongly in evidence and, as with pupils, alternative conceptions abound. This raises serious questions about the current (UK) government strategy of assessing subject knowledge standards which it is expected that all trainee teachers must meet before being allowed entry to the profession. Such findings raise important issues regarding: science teachers’ knowledge of, and need for continuing learning in, science - indeed, it may be that it is the teachers’ valuing of learning and enthusiastic engagement with their students, which is their major contribution to students’ education; the critical stance which students should take in relation to teaching and other sources of ‘authoritative’ information; the importance of negotiating meaning. This paper challenges any simplistic view of the roles of teachers and learners and stresses the belief that although teachers must know about their subjects, they need not know everything. The fact that many graduate scientists do not immediately have ‘the right answers’ to some basic scientific questions need not be perceived as a problem, nor should it undermine their confidence as teachers. [Chem. Educ. Res. Pract. Eur.: 2000, 1, 51-60]