Scientific explanation is an important inquiry practice emphasized in national standards, yet research has neglected the role of the teacher in supporting students' explanation construction. The present study considers whether two teacher practices, modeling explanation and making a framework for explanation explicit to students, predict students' improvement in explanation during a middle-school chemistry unit. Six teachers enacted the unit with a total of 21 classes in urban public schools.

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... coded the teachers' practices during a focal lesson in which they introduced their students to scientific explanation. Regression analyses showed that teachers' scores for the two practices made unique contributions to the prediction of students' posttest scores for one component of the explanation framework, reasoning (i.e. justification for why evidence supports a claim). Furthermore, charting students' explanations across the unit showed that both teacher practices had an immediate impact on students' reasoning in the focal lesson, relative to the pretest, an effect that carried through the unit. We identify avenues for future research that build on our initial effort at mapping teacher practices to student learning outcomes for explanation. Recent science education standards documents (American Association for the Advancement of Science, 1993; National Research Council, 1996) advocate that teachers create learning environments that support student learning of scientific inquiry and the nature of science. Engaging in reading, writing, and talking science is often difficult for middle-school students because science discourse and practice are new to them (Krajcik, Blumenfeld, Marx, Bass, & Fredericks, 1998) . Without support for learning these new ways of knowing, doing, and talking science, students may not relate to science and even actively resist learning it (Lee & Fradd, 1998) . Teachers need to help mediate these ways of knowing science for students by helping them make sense of these practices (Driver, Asoko, Leach, Mortmer, & Scott, 1994).