In this study, we propose an integrated hierarchical model of computational estimation strategies (IHMCES), which can be used to organize a set of computational estimation strategies, used by a group of individuals, in strategy ranges. IHMCES can be used for the description of the repertoire, profile and flexibility of individuals regarding the strategies used. We investigated the computational estimation strategies used by sixty-two 5th grade Greek students. One group of students, were taught with traditional teaching methods while another group, with instructional intervention in computational estimation strategies. Both groups were examined and their computational estimation strategies were analysed. The students' strategy analysis enabled us to identify the strategy ranges used by every student and also describe the changes in every student's strategy range.