This paper reports on an investigation of two inter-related but different matters, one of interest to science education researchers and teachers in general, and the other to those teaching about evolution. The first was motivated by the dilemma facing teachers who want to diagnose learners' prior knowledge before teaching and are concerned about the teaching time needed to identify existing ideas in a valid way. The paper reports on four benefits of adding a confidence scale to a true-false quiz which is quick and easy to use for diagnostic purposes. The second aspect of the study was motivated by the problems experienced by many religious students when they face the challenge of learning about evolution.