This dissertation introduces the construct of worthwhileness as an important aspect of students' practical epistemologies of science (Sandoval, 2005). Specifically, it examines how students conceptualize what makes a scientific research question worthwhile, through a close analysis of the criteria they use for evaluating scientific research questions. Elementary (n=21) and high school students (n=21) participated in this study. As part of semi-structured interviews, students engaged in three novel tasks designed to elicit the epistemic criteria they use to evaluate scientific research questions in a variety of contexts.

Findings indicate that elementary and high school students alike could engage in the practice of evaluating the worth of scientific questions. The criteria they employed included degree of interest, difficulty, and the contribution of questions to knowledge or to solving a problem. The criteria students considered varied by context. Several key differences emerged between the reasoning of the two grade cohorts. High school students tended to place more weight on the contribution of the research question. Also, the criteria reflected in the high school students' judgments of the scientific value of individual questions more closely accorded with the criteria they identified retrospectively as the basis of their judgments. Furthermore, the older cohort more often rationalized the selection and sequence of research questions within a single domain on the basis of epistemic contingency between questions.

How students conceptualize what makes a scientific research question worthwhile constitutes a key aspect of students' epistemic reasoning. It is particularly important to understand how students judge the worthwhilness of scientific research questions given the central epistemic role of research questions in scientific inquiry.

While there is a vast body of research on visual representations, the results do not paint a clear picture of how to use inscriptions to support learning. Part of the difficulty stems from the need for research that investigates the use of inscriptions in classroom learning contexts. Toward this end, there is a small body of work that investigates the role of inscriptions in supporting students' engagement in scientific reasoning practices. Through the development of a case study of expert practice, this dissertation contributes to that literature by examining the potential power of inscriptions as resources for science teaching and learning in the context of a teacher professional development course that aims to support 4th grade teachers' content knowledge around the topic of electric circuits. This study examined the curriculum and video record from one enactment of this course to analyze the affordances of particular representations for supporting conceptual understanding and scientific reasoning practices; examine the facilitator's inscriptional practices that supported collaborative learning; and analyze the interactions among the learners, facilitator, and inscriptions that supported conceptual understanding. This exemplary facilitator successfully used inscriptions to engage learners in scientific reasoning practices that supported their conceptual understanding. She used inscriptions to structure and support discussions that were based on learner-generated ideas, yet led to curriculum-directed conceptual and pedagogical goals. The curriculum provided a series of inscriptional resources that were well suited for the conceptual and scientific reasoning activities that they proposed to support. By using curricular inscriptions to shape the content and form of the discussions, the facilitator created opportunities to learn that were 1) contingent on learner contributions and understanding, and 2) congruent with curricular goals. This work identifies several pedagogical content knowledge demands of supporting scientific reasoning through the use of inscriptions. Beyond knowledge of the conceptual terrain, the facilitator needed to (a) understand the match between particular inscriptions (or types of inscriptions) and the conceptual or scientific reasoning work they can support; (b) understand and interpret learner ideas in relation to the curricular goals; and (c) use inscriptions to make learner ideas available for examination, analysis, revision and discussion in service of the curricular goals.

In recent years a large amount of research has focused on the alternative conceptions about evolution found among secondary and university students, but few studies have investigated younger students' ideas on this subject. The present study examines the alternative conceptions of evolution harbored by second and third-grade students who participated in a summer instructional course that scaffolded the mechanisms of natural selection through cases of microevolution. In order to identify the categories of alternative conceptions that students expressed, 60 sets of pre- and posttest structured interviews were analyzed, and these showed that participants in this study expressed alternative conceptions closely related to those identified in studies conducted using high school and college-age participants. The results demonstrated a variability of alternative conceptions across a range of interview items, and also revealed how contextual features in the assessment tasks may account for the patterns that emerged in students' responses. Students' evocations of alternative conceptions declined after their participation in the instructional course. The analyses of the four case study students, whose pre-and posttest patterns were representative of their cohorts, provided a detailed within-subject look at how these alternative conceptions occurred in the context of the interview items and how they changed from pre- to posttest. These findings have broad relevance to understanding conceptual development in young children and important implications both for considering at how early an age instruction about evolutionary biology should begin and for evaluating the potential long-term impact of a curriculum that targets sources of student difficulty at earlier grade levels.