1. Department of Educational Psychology, University of Minnesota; Minneapolis, Minnesota, USA
2. Department of Mathematics, University of California, Berkeley, California, USA
3. Department of Cognitive Science, University of California, Berkeley, California, USA
4. Statistics Department, Cal Poly San Luis Obispo, California, USA
5. Department of Informatics, University of California, Irvine, California, USA
6. Department of Learning and Instruction, University at Buffalo the State University of New York, Buffalo, New York, USA
7. School of Education, University of California, Berkeley, California, USA
8. Department of Communication, University of California, Los Angeles, California, USA