Evolution is challenging to understand for students. Frequently, students hold coexisting intuitive conceptions based on cognitive biases and scientific conceptions of evolution. For the self-regulation of intuitive and scientific conceptions, metacognitive awareness is fundamental. However, students are mostly unaware of their conceptions. A criteria-referenced self-assessment of one's intuitive and scientific conceptions is one way to develop this metacognitive awareness and enhance conceptual knowledge. We investigated in a study with N = 432 upper secondary students how accurate students are in self-assessing intuitive and scientific conceptions of evolution, which possible explanations for inaccurate self-assessments exist, and which variables are related to self-assessment accuracy (e.g., prior conceptual knowledge, metaconceptual awareness and regulation, and self-efficacy). We found that self-assessment accuracy was moderate, with students self-assessing more intuitive and scientific conceptions than present. Possible explanations for inaccurate self-assessments were incorrect understandings of concepts, excessive self-assessments (of an intuitive concept in a context where it is appropriate; of a scientific concept despite incompleteness), and mix-ups of concepts. Self-assessment accuracy was predicted mainly by prior conceptual knowledge in terms of scientific conceptions and, in some analyses, by prior conceptual knowledge in terms of intuitive conceptions and self-efficacy. The findings have important implications for using self-assessment to develop metaconceptual awareness, for adjusting self-assessments to students' preconditions (e.g., prior knowledge), and for designing teaching approaches in evolution and science education.