Though addressing sources of uncertainty is an important part of doing science, it has largely been neglected in assessing students' scientific argumentation. In this study, we initially defined a scientific argumentation construct in four structural elements consisting of claim, justification, uncertainty qualifier, and uncertainty rationale. We consulted literature to characterize and score different levels of student performances on each of these four argumentation elements. We designed a test comprised of nine scientific argumentation tasks addressing climate change, the search for life in space, and fresh water availability and administered it to 473 students from 9 high schools in the United States. After testing the local dependence and unidimensionality assumptions, we found that the uncertainty qualifier element was not aligned with the other three. After removing items related to uncertainty qualifier, we applied a Rasch analysis based on a Partial Credit Model. Results indicate that (1) claim, justification, and uncertainty rationale items form a unidimensional scale, (2) justification and uncertainty rationale items contribute the most on the unidimensional scientific argumentation scale as they cover much wider ranges of the scale than claim items, (3) average item difficulties increase in the order of claim, justification, and uncertainty rationale, (4) students' elaboration of uncertainty exhibits dual characteristics: self‐assessment of their own knowledge and ability versus scientific assessment of conceptual and empirical errors embedded in investigations, and (5) students who can make warrants between theory and evidence are more likely to think about uncertainty from scientific sources than those who cannot. We identified limitations of this study in terms of science topic coverage and sample selection and made suggestions on how these limitations might have affected results and interpretations. © 2014 Wiley Periodicals, Inc. J Res Sci Teach 51: 581–605, 2014

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This paper describes HASbot, an automated text scoring and real‐time feedback system designed to support student revision of scientific arguments. Students submit open‐ended text responses to explain how their data support claims and how the limitations of their data affect the uncertainty of their explanations. HASbot automatically scores these text responses and returns the scores with feedback to students. Data were collected from 343 middle‐ and high‐school students taught by nine teachers across seven states in the United States. A mixed methods design was applied to investigate (a) how students’ utilization of HASbot impacted their development of uncertainty‐infused scientific arguments; (b) how students used feedback to revise their arguments, and (c) how the current design of HASbot supported or hindered students’ revisions. Paired sample t tests indicate that students made significant gains from pretest to posttest in uncertainty‐infused scientific argumentation, ES = 1.52 SD, p < 0.001. Linear regression analysis results indicate that students' HASbot use significantly contributed to their posttest performance on uncertainty‐infused scientific argumentation while gender, English language learner status, and prior computer experience did not. From the analysis of videos, we identified several affordances and limitations of HASbot.

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