AbstractThis study explores the effectiveness of concept mapping, the learning cycle, expository instruction, and a combination of conceptmapping/learning cycle in promoting conceptual understanding of diffusion and osmosis. Four high school biology classes were taught diffusion and osmosis concepts with the aforementioned treatments. Conceptual understanding was assessed immediately and seven weeks after instruction with the Diffusion and Osmosis Diagnostic Test (DODT). The results indicated the concept mapping/learning cycle and concept mapping treatment groups significantly outperformed the expository treatment group in conceptual understanding of diffusion and osmosis. There was no significant difference among the learning cycle group and other treatments. © 2001 John Wiley & Sons, Inc. Sci Ed 85:615–635, 2001.