We probed the impact of two teaching strategies, "guided inquiry" and "argumentation," on students' conceptual understanding of the conservation of matter. Conservation of matter is a central concept in middle school science curriculum and a prerequisite upon which rests more complex constructs in chemistry. The results indicate that guided inquiry was particularly effective in improving students' conceptual understanding, as evidenced by pre/posttest results and by a skill analysis of in-depth interviews of student dyads. We also discuss how the challenges inherent to educational contexts can undermine the quality and limit the impact of empirical research carried out in many schools. We suggest how these challenges could be met in the emerging infrastructures for change called the Research Schools Network.