TEACHING FOR UNDERSTANDING - A STUDY OF STUDENTS PREINSTRUCTION THEORIES OF MATTER AND A COMPARISON OF THE EFFECTIVENESS OF 2 APPROACHES TOTEACHING ABOUT MATTER AND DENSITY

Thirty 8th-grade students were given an interview and a written test b efore and after a 10-week curriculum unit concerning matter, mass, vol ume, and density. The instruments probed qualitative understandings of matter; ability to differentiate weight and density using qualitative reasoning; formal, quantitative understandings of mass, weight, volum e, and density; and ability to integrate both qualitative and quantita tive reasoning about density. In Part 1 of the study, we examined the organization of student ideas prior to instruction. We found evidence to support our idea that students' qualitative conceptions of matter a nd density were organized in commonsense theories of matter that const rained their understanding of density: Students who believed that all material objects have weight, no matter how small or light the object, were much more likely to have made a beginning differentiation betwee n weight and density than those who did not. We also showed that a qua litative understanding of density emerged prior to a formal, quantitat ive understanding of density, although most students were able to enga ge in explicit proportional reasoning about another, more familiar qua ntity (i.e., sweetness). In Part 2, we compared the effectiveness of t wo teaching approaches. One approach to teaching about matter and dens ity-the standard Introductory Physical Science (IPS) curriculum-emphas ize formal definitions, measurement, and explicit quantitative reasoni ng. Because it asked students to work formally with complex concepts b efore assuring that relevant qualitative understanding was in place, w e designed a modified IFS curriculum that addressed this problem by en couraging students to make their initial assumptions about matter expl icit and open to debate. The modified curriculum also used visual mode ls and qualitative reasoning to help students bridge the gap between t heir starling conceptions and formal, quantitative definitions. We fou nd that both curricula were effective in promoting a good quantitative understanding of mass, volume, and density. The modified curriculum, however, was more effective at restructuring students' qualitative con ceptions and at promoting an integrated understanding of density. Thus , we conclude that science curricula should integrate both qualitative and quantitative reasoning to be effective at promoting conceptual ch ange.