The aim of this paper is to report from a study of the role of instrumented techniques in the students’ learning process. The paper analyses an episode from a case study of students solving differential equations in a CAS environment. The analysis demonstrates how tasks can be designed with the aim to encourage the students to change between the perspective of tool on a mathematical conception and the perspective of object on the conception. Reasons are given in the paper for the assertion, that changing between these two perspectives supports the instrumental genesis as well as the conceptual development.