Developing and Evaluating an Eighth Grade Curriculum Unit That Links Foundational Chemistry to Biological Growth: Using Student Measures to Evaluate the Promise of the Intervention

Students often have trouble understanding key biology ideas, in part because they lack an understanding of foundational chemistry ideas. AAAS [American Association for the Advancement of Science] is collaborating with BSCS [Biological Sciences Curriculum Study] in the development of a curriculum unit that connects core chemistry and biology ideas in order to help eighth grade students build the conceptual foundation needed for high school biology. The unit is designed to engage students in (a) observing phenomena that are explicitly aligned to the targeted ideas and address common student misconceptions and difficulties and (b) using models to help interpret the phenomena in light of the targeted ideas. An initial draft of the unit was pilot tested at two schools in 2011. The results of the pilot test were used to revise the unit. In the spring of 2012, the revised unit and teacher materials were field tested with 677 eighth grade students from four states across the U.S. Pretests and posttests were used to measure the change in students' understanding of chemical reactions, conservation of mass, and biological growth. The data were analyzed using Rasch modeling and the racking and stacking methods. The stacking method showed that, overall, the students made statistically significant gains, suggesting that their understanding of the targeted ideas improved. The racking method showed that the difficulty of most of the items decreased as a result of the intervention, suggesting that the unit successfully covered most of the ideas. An analysis of distractor selections and written explanations of their answer choices showed that fewer students held misconceptions after participating in the unit. These results were used to inform a second round of revisions to the unit. (Contains 10 tables and 3 figures.)