Inquiry-based educational Araitz Uskola contexts including observation of the Moon have been found to facilitate students' understanding of the Sun-Earth-Moon system. However, the role that the collected data play in the knowledge construction process is unclear, as the process that students develop from the collected data has not previously been reported. Use of data is considered one of the three competencies of scientific literacy, and this research focuses on analysing how eighty four pre-service teachers perform it. A five-level scale has been elaborated. Twenty written group reports and 5 oral data discussion have been analysed. Improvement in the students' knowledge, especially in areas that had been reported to be problematic, is observed. Results show that the designed activities and group discussions help students take their data into consideration, establish comparisons and identify patterns. However, difficulties in identifying patterns and especially in explaining their causes arise and are discussed. The role of the teacher in the process of establishing the causes of the identified patterns stands out when oral discussions are analysed. Several interventions of the teacher are found to be the key for the students to be able to use the collected data to construct appropriate scientific knowledge.