This article investigates secondary school teachers' conceptions of mathematics and their teaching practices in the use of graphing calculators in their mathematics classrooms. Case studies on three teacher participants were developed using quantitative and qualitative data that consisted of self-assessments on beliefs in mathematics, observations, surveys on professional and personal technology use and semi-structured interviews. All three teachers had a similar goal of attempting to use the graphing calculators to eliminate mechanical processing time and enhance their students' ability to construct their own learning. The major findings of this article relate to: (1) proficiency with the graphing calculator; (2) a common starting point and (3) integration into the curriculum. This article concludes that factors such as teachers' personal experiences and teaching practices, together with the level of proficiency of the students with the technology, influence how the graphing calculators are used in the mathematics classroom. When graphing calculators are effectively used in the mathematics classroom, they are a powerful tool to assist teachers in providing their students with an environment to help them construct their mathematical knowledge and understanding.