Much of the focus in science education has been on the theoretical constructs and practical implications of conceptual change. History of science, cognitive theory, and alternative conceptions have been used as backdrops for the study of the child's conceptual movement away from naive beliefs about scientific phenomena. In this study, conceptual shifts were proposed as means of examining the process of conceptual change. The relationship of reasoning level, science process skills, gender, and instructional treatment to conceptual shifts in grade 10 biology students were compared. Student reasoning levels were evaluated using the Test of Logical Thinking (TOLT). The Test of Integrated Process Skills (TIPS) was used to measure the students' proficiency with science process skills. Five concept evaluation statements were used to determine the students' understandings of the concepts of diffusion, the cell, circulation, plant food production, and genetics. All instruments were used in a pretest/posttest format. Results indicated that instructional treatment was the only factor that significantly influenced positive shifts in student understanding of a concept. Gender was found to have a moderate influence in an honors class. Reasoning level and prior knowledge did not correlate positively with shifts in student understanding. (Author/CW)