The Conceptual Assessment of Children’s Ideas about Evolution (CACIE) is an interview-based instrument that comprises 20 items about 10 concepts of the evolutionary principles variation, inheritance, and selection. They can be used with six different animal and plant species. The CACIE was piloted with 3 children and then tested with 85 children (1) in cross-sectional interviews and (2) in a test-retest design (n = 14). The children's responses were coded both by the original interviewer and by independent raters. All data is provided within this dataset.