This study investigated the effect of students' ability and type of instructional program, structured and unstructured, on easy and difficult posttest items. Seventh-grade students worked through 14 instructional activities in The Geometer Sketchpad, a dynamic geometry program, and accessed a Geometry tutorial developed to parallel the state geometry standards. Low-ability students scored higher in the less structured program, whereas high- and medium-ability learners performed better in the structured program. High- and medium-ability students outscored low-ability learners by a greater margin on the difficult items than on the easy items. Although their overall performance was poor in both programs, that low-ability learners performed relatively better in the less structured, less traditional, mathematics activities is an encouraging finding for mathematics educators and designers of open-ended learning environments.