About the Authors
Science Education Department, Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, United States of America
Harvard Graduate School of Education, Harvard University, Cambridge, Massachusetts, United States of America
Department of Computer Science, University of Massachusetts, Boston, Massachusetts, United States of America
The authors have declared that no competing interests exist.
Conceived and designed the experiments: MHS GS JMT CC MP. Performed the experiments: MHS CC. Analyzed the data: GS CC. Contributed reagents/materials/analysis tools: MHS JMT CC. Wrote the paper: MHS GS JMT CC MP.