Although teachers' knowledge is thought to contribute to the selection and implementation of mathematical tasks, empirical evidence supporting this claim is scarce. To investigate this relationship and understand its nature, this exploratory study examines the unfolding of tasks in a series of lessons led by 2 elementary school teachers who differed in their level of mathematical knowledge for teaching (MKT). The Mathematical Tasks Framework (MTF) was applied to 9 videotaped lessons from each teacher, with results showing notable differences in the unfolding of tasks in the teachers' lessons. A close examination of data from several other sources--curriculum documents and teachers' general, clinical, and postlesson interviews--suggested a positive association between teachers' MKT and the cognitive level at which tasks are enacted in their lessons. Three tentative hypotheses about specific manifestations of this relationship and directions for future studies situated at the intersection of MKT and MTF are outlined.