The aim of this study was to determine the knowledge of fifth-grade students about the sun, earth, and moon and to examine the fact that this information can be reflected with different measurement tools. A mixed method was used in the research. Quantitative data were collected using a 3-point Likert-type questionnaire and a true-false test; and qualitative data were collected through a fully structured interview and a three-dimensional thinking skills form. It was determined that students knew about the sun, earth, moon, and their properties. However, the students could not provide any data about the distances between the sun, earth, and moon. When the pictures of the students were examined; while very high data were presented for the size and distance related to the sun, earth, and moon, very low data were found for the rotation relationship. The information obtained from the fully structured interview form was determined to reflect the information obtained from the three-dimensional thinking form at a medium level. In addition, according to survey data, the students have a very good level of knowledge and they reflected this information to a good level in the true-false test. To measure the students' level of knowledge, a survey or true-false tests could be used. As a matter of fact, they both offer the same results.