to uncover patterns in data and develop complex scientific arguments supported with evidence (Reiser et al., 2001). They can use scientific visualization tools to analyze primary data sets of atmospheric data and explain patterns of climate change (Edelson, 2001; Edelson, Gordin, and Pea, 1999). There is also some evidence that these project-based experiences can help students learn scientific practices. Kolodner et al. (2003) found that middle school students who practiced inquiry in several project-based science units performed better on the inquiry tasks of scientific practice (as measured by performance assessments) than students from traditional classrooms (Quellmalz et al., 1999). Students in project-based science classrooms performed better than comparison students on designing fair tests, justifying claims with evidence, and generating explanations. They also exhibited more negotiation and collaboration in their group work and a greater tendency to monitor and evaluate their work (Kolodner et al., 2003).
Analyses of students’ content learning also reveal the promise of these approaches for their mastery of scientific principles. Conceptual change researchers have found that across the K-12 grade span, involving children in cycles of model-based reasoning can be a highly effective means of building their deeper conceptual understandings of core scientific principles (Brown and Clement, 1989; Lehrer et al., 2001; Raghavan, Sartoris, and Glaser, 1998; Smith et al., 1997; Stewart, Cartier, and Passmore, 2005; White, 1993; Wiser and Amin, 2001). Problem-based approaches have demonstrated that students succeed in learning complex scientific content as represented in state and national standards, using assessments like the National Assessment of Educational Progress (NAEP) and standardized state tests. For example, Rivet and Krajcik (2004) found that students in a lower income urban district achieved significant gains in both science content (e.g., balanced forces, mechanical advantage) and inquiry process skills, as measured by pre- and posttest achievement items based on state assessments and items from the Trends in International Mathematics and Science Study.
There is also some evidence of the scalability of the approach. Marx and his colleagues (2004) examined the learning gains for 4 project-based units enacted in a school district across 3 years. Again, using curriculum-based test items designed to parallel those on state and NAEP assessments, they found significant learning gains (more than 1 standard deviation in effect sizes) on both content and process items for all four units. These gains persisted and even increased across years of enactment, as the intervention scaled to 98 classrooms and 35 teachers in 14 schools. In more recent work, this research group has compared performance on the high-stakes state assessments for students in project-based classrooms with those of the rest of the district, again focusing on students from the lower socioeconomic distribution in this urban district (Geier et al., in press). Project-based students from seventh and eighth grade achieved higher content and process scores