This research aims to explore the secondary school sixth and seventh graders' length measuring estimation skills developing activities related to the daily life objects. The study is in a qualitative multiple case study model. The universe of the research consisted of the sixth and seventh graders. The sample of the research consisted of 85 students, who were studying at a secondary school in sixth and seventh classes in 2 (two) state schools determined with the purposive sampling method in the 2018-2019 educational year. The maximum variety was ensured for the class level, gender, and mathematics achievement scores; voluntariness for the easily accessible situation. The data were obtained with the scales and semi-structured interview forms prepared during the research process and analyzed descriptively. The research results suggest that the length measuring estimation skills of the secondary school sixth and seventh graders relevant to the daily life objects can be developed with the activities that will develop the students' prior knowledge and skills.