Twenty-three high school biology students were individually administered three conservation tasks (weight, volume, volume displacement). During one semester, they were examined over the course material using published Biological Sciences Curriculum Study (BSCS) Blue Version examination questions which were previously classified as requiring either concrete or formal reasoning for successful completion. Two predictions were made and partially confirmed: (1) a significant relationship exists between a student's ability to conserve and his level of success on the examination items; and (2) nonconserving students do not score above the level of chance success on formal examination items. (Author)