This paper examines two experienced Turkish teachers', Ahmet and Burak, selection and implementation of function problems and relates this to the quality of their students' understanding of this notion. The research findings indicate that regardless of the task quality Ahmet engages, through process-oriented teaching, his students with the notion of function and this encourages them to develop a process conception of function. In contrast, Burak makes reductions, thorough action-oriented teaching, in the task demands. He emphasises rules, procedures and the factual knowledge associated with the representational systems, and this appears to confine his students' understanding to an action conception of function. The evidence suggests that tasks should not be seen as a panacea; it is the teacher's expertise in creating task conditions (for example, establishing links between the ideas and between the representations, using process-oriented language) that may promote student learning. (Contains 2 figures and 7 tables.)