In this study, we investigated the terms and concepts that form part of instruction in the stratum unit, as indicated by elementary school teachers. In particular, we examined the ideas of in-service teachers, focusing on concepts that disappeared or appeared for the first time in the course of revision of the curriculum. We also looked at what was appropriate to teach the stratum unit in the revised curriculum achievement criteria for 2007, 2009, and 2015 and the accompanying textbook inquire activities. In this study, a total of 101 elementary school teachers participated, and the results were as follows. First, the teachers believed that the terms stratum, sedimentary rock, fossil, and rock must be explicitly taught. For the individual rock names, they presented a range of opinions depending on particular rock. Second, because concepts such as rock and fault are fundamental and understandable concepts they thought that the concepts must be learned. Third, students’ ability to perform was the most important criterion in determining appropriate achievement criteria. Fourth, the correlation between the curriculum achievement criteria and the associated inquire activities was very low. As a result of the research, it was found that the terms, concepts, achievement criteria, and inquiry activities that teachers reported needing to teach differ from what is found in currently textbooks. However, in the current curriculum, because learning content and teaching methods are presented too rigorously, teachers cannot teach students in the way they want, which can negatively affect students’ instruction.