The relationship between preferred objects associated with stereotypy, stereotypic behavior, and accuracy of responding during a counting task by a child with autism was analyzed. Object preference was determined by presenting the child with different sets of objects and asking him to choose one. His choices were then rank ordered into three groupslow, medium, and high preference objects. Counting performance within each of the three object groups was then analyzed in a multi-element design, alternating preference groups. Teaching with high-preference objects occasioned more stereotypic behavior and less accurate counting than teaching with medium- and low-preference objects. Thus, there exists the possibility that teaching may be less successful with certain teaching materials, especially if those materials evoke high rates of incompatible behaviors.