The initial phases of design, known as the conceptual design phases, are often associated with hand sketching, while parametric tools are reserved for the later, more developed stages of design. This paper examines the potentials of using parametric tools in the early design phases in comparison to widely utilized hand sketching. It is intended to find out the impacts of using parametric tools on the cognitive behaviors and the satisfaction of self-assessment levels of the designers. An experimental study was conducted with a group of graduate architecture students using Grasshopper, the findings of which are analyzed through a content-oriented coding scheme, together with protocol analyses. Significant differences are found between cognitive behaviors of the participants in using hand sketching and Grasshopper. The findings show that all of the participants consider Grasshopper as a useful conceptual design tool that may be utilized in early design phases, in contrast to its wide popularity in the late stages of design.