This paper focuses on high school mathematics teachers and what they do when they use digital technology in their lessons. It is essentially a discursive paper but it uses data from a project on teachers using technology to illustrate points. The main aim of the paper is to present an holistic account of factors influencing teachers' practice. A secondary aim is to present the integration of technology into lessons as a complex issue. Saxe's four parameter model of goal-linked practice is employed to show how different dimensions of teachers' activities interrelate in this complex undertaking. The paper ends with a consideration of approaches related to Saxe's model.