The present study analyzes students' reasoning strategies for elaboration of conjectures when working in a Dynamic Geometry Environment (DGE). We observed 18 pairs of ten-graders in a private school in Lebanon, while working on open geometrical proof problems using Dynamic Geometry Software (DGS), namely GeoGebra. The analysis revealed three reasoning strategies employed by students. In the first two, the students worked on satisfying the presumed premise of the conjecture in the figure and identifying / validating the conclusion, either by observing the figure at hand (strategy 1) or by dragging the figure to validate the conclusion across different instances (strategy 2). Conversely, in the third strategy, the students worked on satisfying the conclusion of the conjecture in the figure and observing it to identify the premise that corresponds. Each strategy entails the use of different construction tools and types of constructions which affect the correctness of the resulting conjecture.