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 preservice 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.