Students’ and teachers’ misconceptions are an international concern among researchers in science education; they influence how students learn and teachers’ teach knowledge and are a hindrance in the acquisition of accurate knowledge. This paper reports on a literature synthesis of existing research about ecological misconceptions. One means of improving the application of misconceptions involves using diagnostic tests. These form an important component of a broader conceptual toolkit needed to teach science in conceptually accurate ways. Analysis of the results of a diagnostic test, completed by biology students and pre-service teachers in Ireland, revealed the presence of an unacceptably high level of misconceptions and uncovered flaws in students and teachers’ understanding of ecological concepts. A clear link was observed between the misconceptions present in pre-service teachers’ knowledge base and those dominant in students. In this regard, we discuss implications of these findings for teacher education, from pre-service to continuing education.