A number of studies have indicated that police officers trained in the use of the Scottish Executive guidelines for the interviewing of child witnesses do not always adhere to the evidence-based recommendations contained within them. This study explored possible reasons for non-adherence through the qualitative examination of interviewers’ free-text responses to questionnaire items designed to survey their impressions of the guidelines and child interviews in general. Respondents reported many instances of non-adherence or adaptations of recommended practice which they explained and justified in terms of a body of lay or commonsense psychological ‘knowledge’. We argue that such beliefs act as a barrier to guideline implementation and further that the unproblematic, taken-for-granted nature of such justifications reveals the poor standing in the public mind of expert, empirical Psychology. Improving future guideline adherence may therefore require, in addition to the established training in forensic issues, the active challenging of prior beliefs about how the mind works, and to this end possibly also the introduction into training of elements of a general science education.